minor improvement to vdom schema

Author: rmorshea

idom/core/vdom.py

@@ -46,14 +46,16 @@
             "properties": {
                 "source": {"type": "string"},
                 "fallback": {
+                    "type": ["object", "string", "null"],
                     "if": {"not": {"type": "null"}},
                     "then": {"$ref": "#/definitions/elementOrString"},
                 },
             },
             "required": ["source"],
         },
         "elementOrString": {
-            "if": {"not": {"type": "string"}},
+            "type": ["object", "string"],
+            "if": {"type": "object"},
             "then": {"$ref": "#/definitions/element"},
         },
     },

tests/test_core/test_vdom.py

@@ -235,8 +235,8 @@ def test_valid_vdom(value):
             r"data must be array",
         ),
         (
-            {"tagName": "tag", "children": [0]},
-            r"data must be object",
+            {"tagName": "tag", "children": [None]},
+            r"data must be object or string",
         ),
         (
             {"tagName": "tag", "children": [{"tagName": None}]},
@@ -298,7 +298,7 @@ def test_valid_vdom(value):
                 "tagName": "tag",
                 "importSource": {"source": "something", "fallback": 0},
             },
-            r"data must be object",
+            r"data\.fallback must be object or string or null",
         ),
         (
             {