fix(workflows_mcp.engine.executors_file): allow base_path to be None and default to current directory

Changed the type of base_path to accept None and added a validator to default None values to '.' to handle explicit null inputs from agents gracefully.

Author: ibacalu

src/workflows_mcp/engine/executors_file.py

@@ -239,11 +239,18 @@ class ReadFilesInput(BlockInput):
         max_length=50,
     )
 
-    base_path: str = Field(
+    base_path: str | None = Field(
         default=".",
         description="Base directory to search from (relative or absolute). Used with patterns.",
     )
 
+    @field_validator("base_path", mode="before")
+    @classmethod
+    def _default_base_path(cls, v: Any) -> Any:
+        if v is None:
+            return "."
+        return v
+
     mode: Literal["full", "outline", "summary"] | str = Field(
         default="full",
         description=(