Update I1022 to allow functions (#3961)

Author: kddejong

src/cfnlint/rules/functions/SubNotJoin.py

@@ -12,8 +12,6 @@
 
 
 class SubNotJoin(CloudFormationLintRule):
-    """Check if Join is being used with no join characters"""
-
     id = "I1022"
     shortdesc = "Use Sub instead of Join"
     description = (
@@ -35,6 +33,9 @@ def _check_element(self, element):
         return True
 
     def _check_elements(self, elements):
+        if not isinstance(elements, list):
+            return False
+
         for element in elements:
             if not self._check_element(element):
                 return False
@@ -55,7 +56,7 @@ def validate(
 
         if self._check_elements(value[1]):
             yield ValidationError(
-                ("Prefer using Fn::Sub over Fn::Join with an" " empty delimiter"),
+                ("Prefer using Fn::Sub over Fn::Join with an empty delimiter"),
                 path=deque([key, 0]),
                 rule=self,
             )

test/unit/rules/functions/test_sub_not_join.py

@@ -20,6 +20,11 @@ def rule():
 @pytest.fixture
 def template():
     return {
+        "Parameters": {
+            "MyList": {
+                "Type": "CommaDelimitedList",
+            },
+        },
         "Resources": {
             "MyResource": {
                 "Type": "AWS::S3::Bucket",
@@ -37,6 +42,12 @@ def template():
             {"type": "string"},
             [],
         ),
+        (
+            "Valid Fn::Join with a list parameter",
+            {"Fn::Join": ["", {"Ref": "MyList"}]},
+            {"type": "string"},
+            [],
+        ),
         (
             "Invalid Fn::Join with an empty string",
             {"Fn::Join": ["", ["foo", "bar"]]},