fix(core): preserve empty frontmatter permalink semantics

Signed-off-by: phernandez <paul@basicmachines.co>

src/basic_memory/services/entity_service.py

@@ -60,6 +60,11 @@ class EntityWriteResult:
     search_content: str
 
 
+def _frontmatter_permalink(value: object) -> str | None:
+    """Return an explicit frontmatter permalink only when YAML parsed a real string."""
+    return value if isinstance(value, str) and value else None
+
+
 class EntityService(BaseService[EntityModel]):
     """Service for managing entities in the database."""
 
@@ -287,11 +292,13 @@ class EntityService(BaseService[EntityModel]):
                 schema.note_type = content_frontmatter["type"]
 
             if "permalink" in content_frontmatter:
-                content_markdown = self._build_frontmatter_markdown(
-                    schema.title,
-                    schema.note_type,
-                    _coerce_to_string(content_frontmatter["permalink"]),
-                )
+                content_permalink = _frontmatter_permalink(content_frontmatter["permalink"])
+                if content_permalink is not None:
+                    content_markdown = self._build_frontmatter_markdown(
+                        schema.title,
+                        schema.note_type,
+                        content_permalink,
+                    )
 
         # Get unique permalink (prioritizing content frontmatter) unless disabled
         if self.app_config and self.app_config.disable_permalinks:
@@ -394,11 +401,13 @@ class EntityService(BaseService[EntityModel]):
                 schema.note_type = content_frontmatter["type"]
 
             if "permalink" in content_frontmatter:
-                content_markdown = self._build_frontmatter_markdown(
-                    schema.title,
-                    schema.note_type,
-                    _coerce_to_string(content_frontmatter["permalink"]),
-                )
+                content_permalink = _frontmatter_permalink(content_frontmatter["permalink"])
+                if content_permalink is not None:
+                    content_markdown = self._build_frontmatter_markdown(
+                        schema.title,
+                        schema.note_type,
+                        content_permalink,
+                    )
 
         # Check if we need to update the permalink based on content frontmatter (unless disabled)
         new_permalink = entity.permalink  # Default to existing
@@ -525,11 +534,13 @@ class EntityService(BaseService[EntityModel]):
                 schema.note_type = content_frontmatter["type"]
 
             if "permalink" in content_frontmatter:
-                content_markdown = self._build_frontmatter_markdown(
-                    schema.title,
-                    schema.note_type,
-                    _coerce_to_string(content_frontmatter["permalink"]),
-                )
+                content_permalink = _frontmatter_permalink(content_frontmatter["permalink"])
+                if content_permalink is not None:
+                    content_markdown = self._build_frontmatter_markdown(
+                        schema.title,
+                        schema.note_type,
+                        content_permalink,
+                    )
 
         # --- Permalink Resolution ---
         if self.app_config and self.app_config.disable_permalinks:
@@ -668,11 +679,13 @@ class EntityService(BaseService[EntityModel]):
                 update_data["note_type"] = _coerce_to_string(content_frontmatter["type"])
 
             if "permalink" in content_frontmatter:
-                content_markdown = self._build_frontmatter_markdown(
-                    _coerce_to_string(update_data.get("title", entity.title)),
-                    _coerce_to_string(update_data.get("note_type", entity.note_type)),
-                    _coerce_to_string(content_frontmatter["permalink"]),
-                )
+                content_permalink = _frontmatter_permalink(content_frontmatter["permalink"])
+                if content_permalink is not None:
+                    content_markdown = self._build_frontmatter_markdown(
+                        _coerce_to_string(update_data.get("title", entity.title)),
+                        _coerce_to_string(update_data.get("note_type", entity.note_type)),
+                        content_permalink,
+                    )
 
             metadata = normalize_frontmatter_metadata(content_frontmatter or {})
             update_data["entity_metadata"] = {k: v for k, v in metadata.items() if v is not None}

tests/services/test_entity_service_write_result.py

@@ -27,6 +27,28 @@ async def test_create_entity_with_content_returns_full_and_search_content(
     assert result.search_content == "Create body content"
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize("permalink_line", ["permalink:", "permalink: null", 'permalink: ""'])
+async def test_create_entity_ignores_empty_frontmatter_permalink(
+    entity_service, file_service, permalink_line: str
+) -> None:
+    result = await entity_service.create_entity_with_content(
+        EntitySchema(
+            title="Empty Frontmatter Permalink",
+            directory="notes",
+            note_type="note",
+            content=f"---\n{permalink_line}\n---\nCreate body content",
+        )
+    )
+
+    file_path = file_service.get_entity_path(result.entity)
+    file_content, _ = await file_service.read_file(file_path)
+
+    assert result.entity.permalink == "test-project/notes/empty-frontmatter-permalink"
+    assert "permalink: test-project/notes/empty-frontmatter-permalink" in file_content
+    assert "permalink: None" not in file_content
+
+
 @pytest.mark.asyncio
 async def test_update_entity_with_content_returns_full_and_search_content(
     entity_service, file_service