diff --git a/.nextchanges/bundles/schema-comment-nothing-to-update.md b/.nextchanges/bundles/schema-comment-nothing-to-update.md
new file mode 100644
index 0000000000..d7e77b7043
--- /dev/null
+++ b/.nextchanges/bundles/schema-comment-nothing-to-update.md
@@ -0,0 +1 @@
+Fixed `bundle deploy` failing with `Nothing to update` on the direct engine when a schema's, catalog's or volume's comment was set outside the bundle.
diff --git a/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/databricks.yml.tmpl b/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/databricks.yml.tmpl
new file mode 100644
index 0000000000..b7fa6d6d95
--- /dev/null
+++ b/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/databricks.yml.tmpl
@@ -0,0 +1,7 @@
+bundle:
+  name: test-bundle-$UNIQUE_NAME
+
+resources:
+  catalogs:
+    catalog1:
+      name: test-catalog-$UNIQUE_NAME
diff --git a/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/out.test.toml b/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/out.test.toml
new file mode 100644
index 0000000000..8c52d40aa2
--- /dev/null
+++ b/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/out.test.toml
@@ -0,0 +1,3 @@
+Cloud = true
+RequiresUnityCatalog = true
+EnvMatrix.DATABRICKS_BUNDLE_ENGINE = ["direct"]
diff --git a/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/output.txt b/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/output.txt
new file mode 100644
index 0000000000..6ff82f588e
--- /dev/null
+++ b/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/output.txt
@@ -0,0 +1,57 @@
+
+=== Deploy a catalog that does not declare a comment
+>>> [CLI] bundle deploy
+Uploading bundle files to /Workspace/Users/[USERNAME]/.bundle/test-bundle-[UNIQUE_NAME]/default/files...
+Created catalogs.catalog1
+Files: 0 uploaded, 0 deleted
+Resources: 1 created, 0 changed, 0 deleted, 0 unchanged
+
+=== Set the comment out of band, the way Catalog Explorer does
+=== The remote comment is drift, so the plan updates the catalog
+>>> [CLI] bundle plan --output json
+{
+  "action": "update",
+  "remote": "set outside the bundle"
+}
+
+=== Redeploy clears the comment
+>>> [CLI] bundle deploy
+Uploading bundle files to /Workspace/Users/[USERNAME]/.bundle/test-bundle-[UNIQUE_NAME]/default/files...
+Updated catalogs.catalog1
+Files: 0 uploaded, 0 deleted
+Resources: 0 created, 1 changed, 0 deleted, 0 unchanged
+
+=== The comment is gone
+>>> [CLI] api get /api/2.1/unity-catalog/catalogs/test-catalog-[UNIQUE_NAME]
+""
+
+=== Redeploy is a no-op
+>>> [CLI] bundle deploy
+Uploading bundle files to /Workspace/Users/[USERNAME]/.bundle/test-bundle-[UNIQUE_NAME]/default/files...
+Files: 0 uploaded, 0 deleted
+Resources: 0 created, 0 changed, 0 deleted, 1 unchanged
+
+>>> [CLI] bundle destroy --auto-approve
+The following resources will be deleted:
+  delete resources.catalogs.catalog1
+
+All files and directories at the following location will be deleted: /Workspace/Users/[USERNAME]/.bundle/test-bundle-[UNIQUE_NAME]/default
+
+Destroy: 1 deleted
+
+=== The UpdateCatalog payloads the deploys sent
+>>> print_requests.py --method PATCH //unity-catalog/catalogs
+{
+  "method": "PATCH",
+  "path": "/api/2.1/unity-catalog/catalogs/test-catalog-[UNIQUE_NAME]",
+  "body": {
+    "comment": "set outside the bundle"
+  }
+}
+{
+  "method": "PATCH",
+  "path": "/api/2.1/unity-catalog/catalogs/test-catalog-[UNIQUE_NAME]",
+  "body": {
+    "comment": ""
+  }
+}
diff --git a/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/script b/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/script
new file mode 100644
index 0000000000..6f1a938177
--- /dev/null
+++ b/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/script
@@ -0,0 +1,32 @@
+echo "*" > .gitignore
+envsubst < databricks.yml.tmpl > databricks.yml
+
+CATALOG="test-catalog-${UNIQUE_NAME}"
+
+# print_requests.py consumes out.requests.txt, so it has to run after the last
+# request the test makes, which is the destroy below.
+cleanup() {
+    trace $CLI bundle destroy --auto-approve
+
+    title "The UpdateCatalog payloads the deploys sent"
+    trace print_requests.py --method PATCH //unity-catalog/catalogs
+}
+trap cleanup EXIT
+
+title "Deploy a catalog that does not declare a comment"
+trace $CLI bundle deploy
+
+title "Set the comment out of band, the way Catalog Explorer does"
+MSYS_NO_PATHCONV=1 $CLI api patch "/api/2.1/unity-catalog/catalogs/$CATALOG" --json '{"comment":"set outside the bundle"}' > /dev/null
+
+title "The remote comment is drift, so the plan updates the catalog"
+trace $CLI bundle plan --output json | jq '.plan[].changes.comment'
+
+title "Redeploy clears the comment"
+trace $CLI bundle deploy
+
+title "The comment is gone"
+MSYS_NO_PATHCONV=1 trace $CLI api get "/api/2.1/unity-catalog/catalogs/$CATALOG" | jq '.comment'
+
+title "Redeploy is a no-op"
+trace $CLI bundle deploy
diff --git a/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/test.toml b/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/test.toml
new file mode 100644
index 0000000000..ae0b1a870d
--- /dev/null
+++ b/acceptance/bundle/resources/catalogs/drift/comment_out_of_band/test.toml
@@ -0,0 +1,11 @@
+Cloud = true
+RequiresUnityCatalog = true
+
+# UpdateCatalog payload construction is direct-engine-specific.
+EnvMatrix.DATABRICKS_BUNDLE_ENGINE = ["direct"]
+
+Ignore = [
+    ".databricks",
+    ".gitignore",
+    "databricks.yml",
+]
diff --git a/acceptance/bundle/resources/schemas/drift/comment_out_of_band/databricks.yml.tmpl b/acceptance/bundle/resources/schemas/drift/comment_out_of_band/databricks.yml.tmpl
new file mode 100644
index 0000000000..50720b6256
--- /dev/null
+++ b/acceptance/bundle/resources/schemas/drift/comment_out_of_band/databricks.yml.tmpl
@@ -0,0 +1,8 @@
+bundle:
+  name: test-bundle-$UNIQUE_NAME
+
+resources:
+  schemas:
+    schema1:
+      catalog_name: main
+      name: test-schema-$UNIQUE_NAME
diff --git a/acceptance/bundle/resources/schemas/drift/comment_out_of_band/out.test.toml b/acceptance/bundle/resources/schemas/drift/comment_out_of_band/out.test.toml
new file mode 100644
index 0000000000..8c52d40aa2
--- /dev/null
+++ b/acceptance/bundle/resources/schemas/drift/comment_out_of_band/out.test.toml
@@ -0,0 +1,3 @@
+Cloud = true
+RequiresUnityCatalog = true
+EnvMatrix.DATABRICKS_BUNDLE_ENGINE = ["direct"]
diff --git a/acceptance/bundle/resources/schemas/drift/comment_out_of_band/output.txt b/acceptance/bundle/resources/schemas/drift/comment_out_of_band/output.txt
new file mode 100644
index 0000000000..d45016243e
--- /dev/null
+++ b/acceptance/bundle/resources/schemas/drift/comment_out_of_band/output.txt
@@ -0,0 +1,60 @@
+
+=== Deploy a schema that does not declare a comment
+>>> [CLI] bundle deploy
+Uploading bundle files to /Workspace/Users/[USERNAME]/.bundle/test-bundle-[UNIQUE_NAME]/default/files...
+Created schemas.schema1
+Files: 0 uploaded, 0 deleted
+Resources: 1 created, 0 changed, 0 deleted, 0 unchanged
+
+=== Set the comment out of band, the way Catalog Explorer does
+=== The remote comment is drift, so the plan updates the schema
+>>> [CLI] bundle plan --output json
+{
+  "action": "update",
+  "remote": "set outside the bundle"
+}
+
+=== Redeploy clears the comment
+>>> [CLI] bundle deploy
+Uploading bundle files to /Workspace/Users/[USERNAME]/.bundle/test-bundle-[UNIQUE_NAME]/default/files...
+Updated schemas.schema1
+Files: 0 uploaded, 0 deleted
+Resources: 0 created, 1 changed, 0 deleted, 0 unchanged
+
+=== The comment is gone
+>>> [CLI] api get /api/2.1/unity-catalog/schemas/main.test-schema-[UNIQUE_NAME]
+""
+
+=== Redeploy is a no-op
+>>> [CLI] bundle deploy
+Uploading bundle files to /Workspace/Users/[USERNAME]/.bundle/test-bundle-[UNIQUE_NAME]/default/files...
+Files: 0 uploaded, 0 deleted
+Resources: 0 created, 0 changed, 0 deleted, 1 unchanged
+
+>>> [CLI] bundle destroy --auto-approve
+The following resources will be deleted:
+  delete resources.schemas.schema1
+
+This action will result in the deletion of the following UC schemas. Any underlying data may be lost:
+  delete resources.schemas.schema1
+
+All files and directories at the following location will be deleted: /Workspace/Users/[USERNAME]/.bundle/test-bundle-[UNIQUE_NAME]/default
+
+Destroy: 1 deleted
+
+=== The UpdateSchema payloads the deploys sent
+>>> print_requests.py --method PATCH //unity-catalog/schemas
+{
+  "method": "PATCH",
+  "path": "/api/2.1/unity-catalog/schemas/main.test-schema-[UNIQUE_NAME]",
+  "body": {
+    "comment": "set outside the bundle"
+  }
+}
+{
+  "method": "PATCH",
+  "path": "/api/2.1/unity-catalog/schemas/main.test-schema-[UNIQUE_NAME]",
+  "body": {
+    "comment": ""
+  }
+}
diff --git a/acceptance/bundle/resources/schemas/drift/comment_out_of_band/script b/acceptance/bundle/resources/schemas/drift/comment_out_of_band/script
new file mode 100644
index 0000000000..b5f23ec918
--- /dev/null
+++ b/acceptance/bundle/resources/schemas/drift/comment_out_of_band/script
@@ -0,0 +1,32 @@
+echo "*" > .gitignore
+envsubst < databricks.yml.tmpl > databricks.yml
+
+SCHEMA="main.test-schema-${UNIQUE_NAME}"
+
+# print_requests.py consumes out.requests.txt, so it has to run after the last
+# request the test makes, which is the destroy below.
+cleanup() {
+    trace $CLI bundle destroy --auto-approve
+
+    title "The UpdateSchema payloads the deploys sent"
+    trace print_requests.py --method PATCH //unity-catalog/schemas
+}
+trap cleanup EXIT
+
+title "Deploy a schema that does not declare a comment"
+trace $CLI bundle deploy
+
+title "Set the comment out of band, the way Catalog Explorer does"
+MSYS_NO_PATHCONV=1 $CLI api patch "/api/2.1/unity-catalog/schemas/$SCHEMA" --json '{"comment":"set outside the bundle"}' > /dev/null
+
+title "The remote comment is drift, so the plan updates the schema"
+trace $CLI bundle plan --output json | jq '.plan[].changes.comment'
+
+title "Redeploy clears the comment"
+trace $CLI bundle deploy
+
+title "The comment is gone"
+MSYS_NO_PATHCONV=1 trace $CLI api get "/api/2.1/unity-catalog/schemas/$SCHEMA" | jq '.comment'
+
+title "Redeploy is a no-op"
+trace $CLI bundle deploy
diff --git a/acceptance/bundle/resources/schemas/drift/comment_out_of_band/test.toml b/acceptance/bundle/resources/schemas/drift/comment_out_of_band/test.toml
new file mode 100644
index 0000000000..4f7503fc8e
--- /dev/null
+++ b/acceptance/bundle/resources/schemas/drift/comment_out_of_band/test.toml
@@ -0,0 +1,11 @@
+Cloud = true
+RequiresUnityCatalog = true
+
+# UpdateSchema payload construction is direct-engine-specific.
+EnvMatrix.DATABRICKS_BUNDLE_ENGINE = ["direct"]
+
+Ignore = [
+    ".databricks",
+    ".gitignore",
+    "databricks.yml",
+]
diff --git a/acceptance/bundle/resources/volumes/drift/comment_out_of_band/databricks.yml.tmpl b/acceptance/bundle/resources/volumes/drift/comment_out_of_band/databricks.yml.tmpl
new file mode 100644
index 0000000000..084b752f4a
--- /dev/null
+++ b/acceptance/bundle/resources/volumes/drift/comment_out_of_band/databricks.yml.tmpl
@@ -0,0 +1,13 @@
+bundle:
+  name: test-bundle-$UNIQUE_NAME
+
+resources:
+  schemas:
+    schema1:
+      catalog_name: main
+      name: test-schema-$UNIQUE_NAME
+  volumes:
+    volume1:
+      catalog_name: main
+      schema_name: ${resources.schemas.schema1.name}
+      name: test-volume-$UNIQUE_NAME
diff --git a/acceptance/bundle/resources/volumes/drift/comment_out_of_band/out.test.toml b/acceptance/bundle/resources/volumes/drift/comment_out_of_band/out.test.toml
new file mode 100644
index 0000000000..8c52d40aa2
--- /dev/null
+++ b/acceptance/bundle/resources/volumes/drift/comment_out_of_band/out.test.toml
@@ -0,0 +1,3 @@
+Cloud = true
+RequiresUnityCatalog = true
+EnvMatrix.DATABRICKS_BUNDLE_ENGINE = ["direct"]
diff --git a/acceptance/bundle/resources/volumes/drift/comment_out_of_band/output.txt b/acceptance/bundle/resources/volumes/drift/comment_out_of_band/output.txt
new file mode 100644
index 0000000000..c1e1f119fa
--- /dev/null
+++ b/acceptance/bundle/resources/volumes/drift/comment_out_of_band/output.txt
@@ -0,0 +1,68 @@
+
+=== Deploy a volume that does not declare a comment
+>>> [CLI] bundle deploy
+Uploading bundle files to /Workspace/Users/[USERNAME]/.bundle/test-bundle-[UNIQUE_NAME]/default/files...
+Created schemas.schema1
+Created volumes.volume1
+Files: 0 uploaded, 0 deleted
+Resources: 2 created, 0 changed, 0 deleted, 0 unchanged
+
+=== Set the comment out of band, the way Catalog Explorer does
+=== The remote comment is drift, so the plan updates the volume
+>>> [CLI] bundle plan --output json
+{
+  "action": "update",
+  "remote": "set outside the bundle"
+}
+
+=== Redeploy clears the comment
+>>> [CLI] bundle deploy
+Uploading bundle files to /Workspace/Users/[USERNAME]/.bundle/test-bundle-[UNIQUE_NAME]/default/files...
+Updated volumes.volume1
+Files: 0 uploaded, 0 deleted
+Resources: 0 created, 1 changed, 0 deleted, 1 unchanged
+
+=== The comment is gone
+>>> [CLI] api get /api/2.1/unity-catalog/volumes/main.test-schema-[UNIQUE_NAME].test-volume-[UNIQUE_NAME]
+""
+
+=== Redeploy is a no-op
+>>> [CLI] bundle deploy
+Uploading bundle files to /Workspace/Users/[USERNAME]/.bundle/test-bundle-[UNIQUE_NAME]/default/files...
+Files: 0 uploaded, 0 deleted
+Resources: 0 created, 0 changed, 0 deleted, 2 unchanged
+
+>>> [CLI] bundle destroy --auto-approve
+The following resources will be deleted:
+  delete resources.schemas.schema1
+  delete resources.volumes.volume1
+
+This action will result in the deletion of the following UC schemas. Any underlying data may be lost:
+  delete resources.schemas.schema1
+
+This action will result in the deletion of the following volumes.
+For managed volumes, the files stored in the volume are also deleted from your
+cloud tenant within 30 days. For external volumes, the metadata about the volume
+is removed from the catalog, but the underlying files are not deleted:
+  delete resources.volumes.volume1
+
+All files and directories at the following location will be deleted: /Workspace/Users/[USERNAME]/.bundle/test-bundle-[UNIQUE_NAME]/default
+
+Destroy: 2 deleted
+
+=== The UpdateVolume payloads the deploys sent
+>>> print_requests.py --method PATCH //unity-catalog/volumes
+{
+  "method": "PATCH",
+  "path": "/api/2.1/unity-catalog/volumes/main.test-schema-[UNIQUE_NAME].test-volume-[UNIQUE_NAME]",
+  "body": {
+    "comment": "set outside the bundle"
+  }
+}
+{
+  "method": "PATCH",
+  "path": "/api/2.1/unity-catalog/volumes/main.test-schema-[UNIQUE_NAME].test-volume-[UNIQUE_NAME]",
+  "body": {
+    "comment": ""
+  }
+}
diff --git a/acceptance/bundle/resources/volumes/drift/comment_out_of_band/script b/acceptance/bundle/resources/volumes/drift/comment_out_of_band/script
new file mode 100644
index 0000000000..c176403ba0
--- /dev/null
+++ b/acceptance/bundle/resources/volumes/drift/comment_out_of_band/script
@@ -0,0 +1,32 @@
+echo "*" > .gitignore
+envsubst < databricks.yml.tmpl > databricks.yml
+
+VOLUME="main.test-schema-${UNIQUE_NAME}.test-volume-${UNIQUE_NAME}"
+
+# print_requests.py consumes out.requests.txt, so it has to run after the last
+# request the test makes, which is the destroy below.
+cleanup() {
+    trace $CLI bundle destroy --auto-approve
+
+    title "The UpdateVolume payloads the deploys sent"
+    trace print_requests.py --method PATCH //unity-catalog/volumes
+}
+trap cleanup EXIT
+
+title "Deploy a volume that does not declare a comment"
+trace $CLI bundle deploy
+
+title "Set the comment out of band, the way Catalog Explorer does"
+MSYS_NO_PATHCONV=1 $CLI api patch "/api/2.1/unity-catalog/volumes/$VOLUME" --json '{"comment":"set outside the bundle"}' > /dev/null
+
+title "The remote comment is drift, so the plan updates the volume"
+trace $CLI bundle plan --output json | jq '.plan["resources.volumes.volume1"].changes.comment'
+
+title "Redeploy clears the comment"
+trace $CLI bundle deploy
+
+title "The comment is gone"
+MSYS_NO_PATHCONV=1 trace $CLI api get "/api/2.1/unity-catalog/volumes/$VOLUME" | jq '.comment'
+
+title "Redeploy is a no-op"
+trace $CLI bundle deploy
diff --git a/acceptance/bundle/resources/volumes/drift/comment_out_of_band/test.toml b/acceptance/bundle/resources/volumes/drift/comment_out_of_band/test.toml
new file mode 100644
index 0000000000..bec056028b
--- /dev/null
+++ b/acceptance/bundle/resources/volumes/drift/comment_out_of_band/test.toml
@@ -0,0 +1,11 @@
+Cloud = true
+RequiresUnityCatalog = true
+
+# UpdateVolume payload construction is direct-engine-specific.
+EnvMatrix.DATABRICKS_BUNDLE_ENGINE = ["direct"]
+
+Ignore = [
+    ".databricks",
+    ".gitignore",
+    "databricks.yml",
+]
diff --git a/bundle/direct/dresources/catalog.go b/bundle/direct/dresources/catalog.go
index 604100e92d..54afbb1fd3 100644
--- a/bundle/direct/dresources/catalog.go
+++ b/bundle/direct/dresources/catalog.go
@@ -62,7 +62,7 @@ func (r *ResourceCatalog) DoUpdate(ctx context.Context, id string, config *catal
 		Options:                      config.Options,
 		Owner:                        "", // Not supported by DABs
 		Properties:                   config.Properties,
-		ForceSendFields:              utils.FilterFields[catalog.UpdateCatalog](config.ForceSendFields, "EnablePredictiveOptimization", "IsolationMode", "Owner"),
+		ForceSendFields:              forceSendComment(utils.FilterFields[catalog.UpdateCatalog](config.ForceSendFields, "EnablePredictiveOptimization", "IsolationMode", "Owner")),
 	}
 
 	response, err := r.client.Catalogs.Update(ctx, updateRequest)
@@ -86,7 +86,7 @@ func (r *ResourceCatalog) DoUpdateWithID(ctx context.Context, id string, config
 		Options:                      config.Options,
 		Owner:                        "", // Not supported by DABs
 		Properties:                   config.Properties,
-		ForceSendFields:              utils.FilterFields[catalog.UpdateCatalog](config.ForceSendFields, "EnablePredictiveOptimization", "IsolationMode", "Owner"),
+		ForceSendFields:              forceSendComment(utils.FilterFields[catalog.UpdateCatalog](config.ForceSendFields, "EnablePredictiveOptimization", "IsolationMode", "Owner")),
 	}
 
 	if config.Name != id {
diff --git a/bundle/direct/dresources/schema.go b/bundle/direct/dresources/schema.go
index 24c82ceb6a..ea406e2684 100644
--- a/bundle/direct/dresources/schema.go
+++ b/bundle/direct/dresources/schema.go
@@ -56,7 +56,7 @@ func (r *ResourceSchema) DoUpdate(ctx context.Context, id string, config *catalo
 		NewName:                      "", // We recreate schemas on name change intentionally.
 		Owner:                        "", // Not supported by DABs
 		Properties:                   config.Properties,
-		ForceSendFields:              utils.FilterFields[catalog.UpdateSchema](config.ForceSendFields, "EnablePredictiveOptimization", "NewName", "Owner"),
+		ForceSendFields:              forceSendComment(utils.FilterFields[catalog.UpdateSchema](config.ForceSendFields, "EnablePredictiveOptimization", "NewName", "Owner")),
 	}
 
 	response, err := r.client.Schemas.Update(ctx, updateRequest)
diff --git a/bundle/direct/dresources/util.go b/bundle/direct/dresources/util.go
index fc68f3ea37..51db2a5dcd 100644
--- a/bundle/direct/dresources/util.go
+++ b/bundle/direct/dresources/util.go
@@ -65,3 +65,14 @@ func collectLeafUpdatePathsWithPrefix(changes Changes, prefix string) []string {
 	slices.Sort(paths)
 	return paths
 }
+
+// forceSendComment adds Comment to a ForceSendFields list, so a comment the config no
+// longer sets serializes as "" instead of being dropped by omitempty.
+//
+// The UC update APIs answer a PATCH that carries no field with "Nothing to update" (400)
+// rather than treating it as a no-op. A resource whose only updatable field is its comment
+// would otherwise become undeployable the moment someone sets a description on it outside
+// the bundle. Sending the empty value also makes clearing such a comment actually happen.
+func forceSendComment(forceSendFields []string) []string {
+	return append(forceSendFields, "Comment")
+}
diff --git a/bundle/direct/dresources/volume.go b/bundle/direct/dresources/volume.go
index 6c96e66ecc..ae56bb4f21 100644
--- a/bundle/direct/dresources/volume.go
+++ b/bundle/direct/dresources/volume.go
@@ -55,7 +55,7 @@ func (r *ResourceVolume) DoUpdate(ctx context.Context, id string, config *catalo
 		NewName: "", // Not supported by Update(). Needs DoUpdateWithID()
 		Owner:   "", // Not supported by DABs
 
-		ForceSendFields: utils.FilterFields[catalog.UpdateVolumeRequestContent](config.ForceSendFields, "NewName", "Owner"),
+		ForceSendFields: forceSendComment(utils.FilterFields[catalog.UpdateVolumeRequestContent](config.ForceSendFields, "NewName", "Owner")),
 	}
 
 	nameFromID, err := getNameFromID(id)
@@ -87,7 +87,7 @@ func (r *ResourceVolume) DoUpdateWithID(ctx context.Context, id string, config *
 		NewName: "", // Initialized below if needed
 		Owner:   "", // Not supported by DABs
 
-		ForceSendFields: utils.FilterFields[catalog.UpdateVolumeRequestContent](config.ForceSendFields, "Owner"),
+		ForceSendFields: forceSendComment(utils.FilterFields[catalog.UpdateVolumeRequestContent](config.ForceSendFields, "Owner")),
 	}
 
 	items := strings.Split(id, ".")
diff --git a/libs/testserver/catalogs.go b/libs/testserver/catalogs.go
index 1d0bc06568..4c1c864b1a 100644
--- a/libs/testserver/catalogs.go
+++ b/libs/testserver/catalogs.go
@@ -88,6 +88,11 @@ func (s *FakeWorkspace) CatalogsUpdate(req Request, name string) Response {
 		}
 	}
 
+	fields, errResponse := parseUCUpdate(req.Body, "UpdateCatalog")
+	if errResponse != nil {
+		return *errResponse
+	}
+
 	var updateRequest catalog.UpdateCatalog
 	if err := json.Unmarshal(req.Body, &updateRequest); err != nil {
 		return Response{
@@ -96,9 +101,13 @@ func (s *FakeWorkspace) CatalogsUpdate(req Request, name string) Response {
 		}
 	}
 
-	// Update only the fields that can be updated
-	if updateRequest.Comment != "" {
+	// Update only the fields that can be updated. Comment is keyed off presence rather
+	// than a non-empty value so an explicit empty comment clears it, the way UC does.
+	if _, ok := fields["comment"]; ok {
 		existing.Comment = updateRequest.Comment
+		// UC echoes a comment once it has been set, including when it was set to "",
+		// so keep it in the response rather than letting omitempty drop it.
+		existing.ForceSendFields = append(existing.ForceSendFields, "Comment")
 	}
 	if updateRequest.CustomMaxRetentionHours != 0 {
 		existing.CustomMaxRetentionHours = updateRequest.CustomMaxRetentionHours
diff --git a/libs/testserver/fake_workspace.go b/libs/testserver/fake_workspace.go
index 1caec84d1e..d5af448c31 100644
--- a/libs/testserver/fake_workspace.go
+++ b/libs/testserver/fake_workspace.go
@@ -5,6 +5,7 @@ import (
 	"encoding/binary"
 	"encoding/json"
 	"fmt"
+	"net/http"
 	"os"
 	"path"
 	"path/filepath"
@@ -254,6 +255,37 @@ func (s *FakeWorkspace) LockUnlock() func() {
 	return func() { s.mu.Unlock() }
 }
 
+// parseUCUpdate decodes a Unity Catalog update payload into its raw fields. It returns a
+// rejection response when the body carries no field to act on: UC answers such a PATCH with
+// "<operation> Nothing to update." (400) rather than treating it as a no-op. A key set to
+// null does not count. Verified against a real workspace for schemas, volumes and catalogs:
+// {} and {"comment": null} are rejected, while {"comment": ""} and
+// {"custom_max_retention_hours": 0} are accepted.
+func parseUCUpdate(body []byte, operation string) (map[string]json.RawMessage, *Response) {
+	var fields map[string]json.RawMessage
+
+	if err := json.Unmarshal(body, &fields); err != nil {
+		return nil, &Response{
+			Body:       fmt.Sprintf("internal error: %s", err),
+			StatusCode: http.StatusInternalServerError,
+		}
+	}
+
+	for _, value := range fields {
+		if string(value) != "null" {
+			return fields, nil
+		}
+	}
+
+	return nil, &Response{
+		StatusCode: http.StatusBadRequest,
+		Body: map[string]string{
+			"error_code": "INVALID_PARAMETER_VALUE",
+			"message":    operation + " Nothing to update.",
+		},
+	}
+}
+
 // Generic functions to handle map operations
 func MapGet[T any](w *FakeWorkspace, collection map[string]T, key string) Response {
 	defer w.LockUnlock()()
diff --git a/libs/testserver/schemas.go b/libs/testserver/schemas.go
index 66d23a3011..72fd456427 100644
--- a/libs/testserver/schemas.go
+++ b/libs/testserver/schemas.go
@@ -80,6 +80,11 @@ func (s *FakeWorkspace) SchemasUpdate(req Request, name string) Response {
 		}
 	}
 
+	fields, errResponse := parseUCUpdate(req.Body, "UpdateSchema")
+	if errResponse != nil {
+		return *errResponse
+	}
+
 	var schemaUpdate catalog.SchemaInfo
 
 	if err := json.Unmarshal(req.Body, &schemaUpdate); err != nil {
@@ -97,6 +102,13 @@ func (s *FakeWorkspace) SchemasUpdate(req Request, name string) Response {
 		}
 	}
 
+	// mergo skips zero values, so an explicit empty comment would leave the stored one in
+	// place. UC clears it instead. Comment is the only field UpdateSchema can clear at
+	// all: clearing properties needs an empty or null map, which the check above rejects.
+	if _, ok := fields["comment"]; ok {
+		existing.Comment = schemaUpdate.Comment
+	}
+
 	existing.UpdatedAt = nowMilli()
 	existing.UpdatedBy = s.CurrentUser().UserName
 
diff --git a/libs/testserver/volumes.go b/libs/testserver/volumes.go
index 88eae7ac02..5a6923b0e8 100644
--- a/libs/testserver/volumes.go
+++ b/libs/testserver/volumes.go
@@ -76,6 +76,11 @@ func (s *FakeWorkspace) VolumesUpdate(req Request, fullname string) Response {
 		}
 	}
 
+	fields, errResponse := parseUCUpdate(req.Body, "UpdateVolume")
+	if errResponse != nil {
+		return *errResponse
+	}
+
 	var request catalog.UpdateVolumeRequestContent
 
 	if err := json.Unmarshal(req.Body, &request); err != nil {
@@ -85,8 +90,13 @@ func (s *FakeWorkspace) VolumesUpdate(req Request, fullname string) Response {
 		}
 	}
 
-	if request.Comment != "" {
+	// Keyed off presence rather than a non-empty value so an explicit empty comment
+	// clears the stored one, the way UC does.
+	if _, ok := fields["comment"]; ok {
 		existing.Comment = request.Comment
+		// UC echoes a comment once it has been set, including when it was set to "",
+		// so keep it in the response rather than letting omitempty drop it.
+		existing.ForceSendFields = append(existing.ForceSendFields, "Comment")
 	}
 
 	if request.Owner != "" {