fix: OutputAdapter from_dict with custom_filters None (#8173)

Co-authored-by: Marie-Luise Klaus <marieluise.klaus@deepset.ai>

haystack/components/converters/output_adapter.py

@@ -139,8 +139,13 @@ class OutputAdapter:
         """
         init_params = data.get("init_parameters", {})
         init_params["output_type"] = deserialize_type(init_params["output_type"])
-        for name, filter_func in init_params.get("custom_filters", {}).items():
-            init_params["custom_filters"][name] = deserialize_callable(filter_func) if filter_func else None
+
+        custom_filters = init_params.get("custom_filters", {})
+        if custom_filters:
+            init_params["custom_filters"] = {
+                name: deserialize_callable(filter_func) if filter_func else None
+                for name, filter_func in custom_filters.items()
+            }
         return default_from_dict(cls, data)
 
     def _extract_variables(self, env: SandboxedEnvironment) -> Set[str]:

releasenotes/notes/fix-output-adapter-from_dict-custom-filters-none-70705cbb474fe982.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Fix Output Adapter from_dict method when custom_filters value is None.

test/components/converters/test_output_adapter.py

@@ -129,6 +129,22 @@ class TestOutputAdapter:
         # invoke the custom filter to check if it is deserialized correctly
         assert deserialized_adapter.custom_filters["custom_filter"]("test") == "TEST"
 
+    def test_output_adapter_from_dict_custom_filters_none(self):
+        component = OutputAdapter.from_dict(
+            data={
+                "type": "haystack.components.converters.output_adapter.OutputAdapter",
+                "init_parameters": {
+                    "template": "{{ documents[0].content}}",
+                    "output_type": "str",
+                    "custom_filters": None,
+                },
+            }
+        )
+
+        assert component.template == "{{ documents[0].content}}"
+        assert component.output_type == str
+        assert component.custom_filters == {}
+
     def test_output_adapter_in_pipeline(self):
         @component
         class DocumentProducer: