fix: Handle null, empty, and string 'None' title in markdown frontmatter (#387)

This fixes a bug where entities with invalid title values in frontmatter
caused SQL INSERT failures due to NOT NULL constraint violations.

The parser now properly falls back to the filename stem when title is:
- None/null (YAML null value)
- Empty string
- The string "None" (common in user templates)

This matches the existing pattern used for type field validation.

Co-authored-by: Paul Hernandez <phernandez@users.noreply.github.com>

Author: github-actions[bot]

src/basic_memory/markdown/entity_parser.py

@@ -129,8 +129,13 @@ async def parse_file_content(self, absolute_path, file_content):
         file_stats = absolute_path.stat()
         metadata = post.metadata
 
-        # Ensure required fields have defaults (issue #184)
-        metadata["title"] = post.metadata.get("title", absolute_path.stem)
+        # Ensure required fields have defaults (issue #184, #387)
+        # Handle title - use default if missing, None/null, empty, or string "None"
+        title = post.metadata.get("title")
+        if not title or title == "None":
+            metadata["title"] = absolute_path.stem
+        else:
+            metadata["title"] = title
         # Handle type - use default if missing OR explicitly set to None/null
         entity_type = post.metadata.get("type")
         metadata["type"] = entity_type if entity_type is not None else "note"

tests/markdown/test_entity_parser_error_handling.py

@@ -183,6 +183,84 @@ async def test_parse_file_with_null_entity_type(tmp_path):
     assert result.frontmatter.title == "Test File"
 
 
+@pytest.mark.asyncio
+async def test_parse_file_with_null_title(tmp_path):
+    """Test that files with explicit null title get default from filename (issue #387)."""
+    # Create a file with null title
+    test_file = tmp_path / "null_title.md"
+    content = dedent(
+        """
+        ---
+        title: null
+        type: note
+        ---
+        # Content
+        """
+    ).strip()
+    test_file.write_text(content)
+
+    # Parse the file
+    parser = EntityParser(tmp_path)
+    result = await parser.parse_file(test_file)
+
+    # Should have default title from filename even when explicitly set to null
+    assert result is not None
+    assert result.frontmatter.title == "null_title"  # Default from filename
+    assert result.frontmatter.type == "note"
+
+
+@pytest.mark.asyncio
+async def test_parse_file_with_empty_title(tmp_path):
+    """Test that files with empty title get default from filename (issue #387)."""
+    # Create a file with empty title
+    test_file = tmp_path / "empty_title.md"
+    content = dedent(
+        """
+        ---
+        title:
+        type: note
+        ---
+        # Content
+        """
+    ).strip()
+    test_file.write_text(content)
+
+    # Parse the file
+    parser = EntityParser(tmp_path)
+    result = await parser.parse_file(test_file)
+
+    # Should have default title from filename when title is empty
+    assert result is not None
+    assert result.frontmatter.title == "empty_title"  # Default from filename
+    assert result.frontmatter.type == "note"
+
+
+@pytest.mark.asyncio
+async def test_parse_file_with_string_none_title(tmp_path):
+    """Test that files with string 'None' title get default from filename (issue #387)."""
+    # Create a file with string "None" as title (common in templates)
+    test_file = tmp_path / "template_file.md"
+    content = dedent(
+        """
+        ---
+        title: "None"
+        type: note
+        ---
+        # Content
+        """
+    ).strip()
+    test_file.write_text(content)
+
+    # Parse the file
+    parser = EntityParser(tmp_path)
+    result = await parser.parse_file(test_file)
+
+    # Should have default title from filename when title is string "None"
+    assert result is not None
+    assert result.frontmatter.title == "template_file"  # Default from filename
+    assert result.frontmatter.type == "note"
+
+
 @pytest.mark.asyncio
 async def test_parse_valid_file_still_works(tmp_path):
     """Test that valid files with proper frontmatter still parse correctly."""