Some quick and dirty changes. Adds notion of elements with undefined keyTo and keyFrom (arrays items), updates tests to reflect the changes, and modifies some error path code to better match VSCode JSON schema linting behavior.

Author: tbrockman

.vscode/settings.json

@@ -3,5 +3,8 @@
   "editor.formatOnSave": true,
   "files.insertFinalNewline": true,
   "coverage-gutters.coverageBaseDir": "**",
-  "coverage-gutters.coverageFileNames": ["clover.xml"]
+  "coverage-gutters.coverageFileNames": ["clover.xml"],
+  "[json]": {
+    "editor.defaultFormatter": "vscode.json-language-features"
+  }
 }