Catch TypeError instead of Exception when checking ability to serialize to JSON.

nucypher/policy/conditions/evm.py

@@ -356,6 +356,7 @@ class ContractCondition(RPCCondition):
         super().__init__(condition_type=condition_type, method=method, *args, **kwargs)
 
     def _validate_method(self, method):
+        # overrides validate method used by rpc superclass
         return method
 
     def _validate_expected_return_type(self) -> None:

nucypher/policy/conditions/lingo.py

@@ -245,7 +245,7 @@ class ReturnValueTest:
 
             try:
                 json.dumps(value)
-            except Exception:
+            except TypeError:
                 raise self.InvalidExpression(
                     f"No JSON serializable equivalent found for type {type(value)}"
                 )