Ensure removing Abbreviations does not raise an error.

docs/changelog.md

@@ -23,6 +23,7 @@ See the [Contributing Guide](contributing.md) for details.
 
 ### Fixed
 
+* Ensure removing Abbreviations does not raise an error (#1634).
 * Fix an issue with excessive backtracking when matching inline code blocks (#1617).
 * `md_in_html` now honors tags added to `Markdown.block_level_elements` after
   the extension is loaded (#1246).

markdown/extensions/abbr.py

@@ -162,7 +162,7 @@ def run(self, parent: etree.Element, blocks: list[str]) -> bool:
             title = m.group('title').strip()
             if title and abbr:
                 if title == "''" or title == '""':
-                    self.abbrs.pop(abbr)
+                    self.abbrs.pop(abbr, None)
                 else:
                     self.abbrs[abbr] = title
                 if block[m.end():].strip():

tests/test_syntax/extensions/test_abbr.py

@@ -211,6 +211,56 @@ def test_abbr_glossary_2(self):
             extensions=[abbr_ext]
         )
 
+    def test_abbr_glossary_override(self):
+
+        glossary = {
+            "HTML": "Hyper Text Markup Language",
+            "W3C": "World Wide Web Consortium"
+        }
+
+        self.assertMarkdownRenders(
+            self.dedent(
+                """
+                HTML
+                W3C
+
+                *[HTML]: ''
+                *[W3C]: Something Else
+                """
+            ),
+            self.dedent(
+                """
+                <p>HTML
+                <abbr title="Something Else">W3C</abbr></p>
+                """
+            ),
+            extensions=[AbbrExtension(glossary=glossary)]
+        )
+
+    def test_abbr_override_not_in_glossary(self):
+
+        glossary = {
+            "W3C": "World Wide Web Consortium"
+        }
+
+        self.assertMarkdownRenders(
+            self.dedent(
+                """
+                HTML
+                W3C
+
+                *[HTML]: ''
+                """
+            ),
+            self.dedent(
+                """
+                <p>HTML
+                <abbr title="World Wide Web Consortium">W3C</abbr></p>
+                """
+            ),
+            extensions=[AbbrExtension(glossary=glossary)]
+        )
+
     def test_abbr_nested(self):
         self.assertMarkdownRenders(
             self.dedent(