fix: post process openapi schema to allow null types (#214)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

tap_dbt/client.py

@@ -71,7 +71,16 @@ def schema(self) -> dict[str, t.Any]:
         Returns:
             The schema for this stream.
         """
-        return self._resolve_openapi_ref()
+        openapi_response = self._resolve_openapi_ref()
+
+        for property_schema in openapi_response["properties"].values():
+            if property_schema.get("nullable"):
+                if isinstance(property_schema["type"], list):
+                    property_schema["type"].append("null")
+                else:
+                    property_schema["type"] = [property_schema["type"], "null"]
+
+        return openapi_response
 
     @property
     @abstractmethod