Make sure val is iterable (#2665)

* Make sure val is iterable

Author: kddejong

src/cfnlint/languageExtensions.py

@@ -29,7 +29,11 @@ def validate_pseudo_parameters(
     ):
         if isinstance(fn_object_val, dict):
             ref = "Ref"
-            ref_list = [val[ref] for key, val in fn_object_val.items() if ref in val]
+            ref_list = [
+                val[ref]
+                for _, val in fn_object_val.items()
+                if hasattr(val, "__iter__") and ref in val
+            ]
             for ref in ref_list:
                 if ref in pseudo_params:
                     message = (

test/fixtures/templates/good/functions_findinmap_default_value.yaml

@@ -75,6 +75,7 @@ Resources:
         - 'Fn::ToJsonString':
             To: Json
             String: Function
+            Value: 1
         - SecondKey1
         - DefaultValue: Mesh2
   Mesh3: