fix: handle None/empty edge cases in SearchFilter and Update.set() (#282)

- SearchFilter now accepts `value: str | None` to handle cases where
  no search parameter is provided (fixes #281)
- Update.set() now returns self unchanged when called with empty
  args/kwargs, supporting Pydantic/msgspec exclude_unset patterns (fixes #279)

Both fixes follow the principle of handling edge cases gracefully at
the source rather than requiring defensive checks everywhere.

Author: cofin

sqlspec/builder/_dml.py

@@ -310,6 +310,8 @@ def _process_update_value(self, val: Any, col: Any) -> exp.Expression:
         return placeholder
 
     def set(self, *args: Any, **kwargs: Any) -> Self:
+        if not args and not kwargs:
+            return self
         current_expr = self.get_expression()
         if current_expr is None:
             self.set_expression(exp.Update())

sqlspec/core/filters.py

@@ -658,7 +658,7 @@ class SearchFilter(StatementFilter):
 
     __slots__ = ("_field_name", "_ignore_case", "_value")
 
-    def __init__(self, field_name: str | set[str], value: str, ignore_case: bool | None = False) -> None:
+    def __init__(self, field_name: str | set[str], value: str | None, ignore_case: bool | None = False) -> None:
         self._field_name = field_name
         self._value = value
         self._ignore_case = ignore_case
@@ -668,7 +668,7 @@ def field_name(self) -> str | set[str]:
         return self._field_name
 
     @property
-    def value(self) -> str:
+    def value(self) -> str | None:
         return self._value
 
     @property

sqlspec/extensions/litestar/providers.py

@@ -226,12 +226,7 @@ def provide_search_filter(
             ),
         ) -> SearchFilter:
             field_names = set(search_fields.split(",")) if isinstance(search_fields, str) else set(search_fields)
-
-            return SearchFilter(
-                field_name=field_names,
-                value=search_string,  # type: ignore[arg-type]
-                ignore_case=ignore_case or False,
-            )
+            return SearchFilter(field_name=field_names, value=search_string, ignore_case=ignore_case or False)
 
         filters[dep_defaults.SEARCH_FILTER_DEPENDENCY_KEY] = Provide(provide_search_filter, sync_to_thread=False)