[backend][experimentmodel] Do not assume map content

The model will also be used on new experiments which
are empty.

beat/editor/backend/experimentmodel.py

@@ -119,12 +119,11 @@ class AlgorithmData:
     def dataformat_for_endpoint(self, endpoint: str) -> str:
         for alg_in, block_in in self.input_mapping.items():
             if block_in == endpoint:
-                return self.input_type_map[alg_in]
+                return self.input_type_map.get(alg_in, "")
 
         for alg_out, block_out in self.output_mapping.items():
             if block_out == endpoint:
-                return self.output_type_map[alg_out]
-
+                return self.output_type_map.get(alg_out, "")
         return ""
 
     def __repr__(self) -> str: