Wrong output produced for special characters

When using the method ComplexElement.makeStringElement(String value), more special characters need to be checked for. Currently only [,{,\,",\n are searched for, but the full list includes :,,,#,[,{,",\n

Furthermore, it should be checked for null and blank values.

Suggested fix in Helpers.jrag:

   // --- helper methods for put/add ---
   protected SimpleElement ComplexElement.makeStringElement(String value) {
+    if (value == null || value.equals("null")) {
+      return StringElement.of("null");
+    }
+    if (value.isBlank()) {
+      return StringElement.of(value);
+    }
     // simple test, check for special characters
-    return containsAny(value, "[{\"\n") ?
+    return containsAny(value, ":#,[{\"\n") ?
       StringElement.of(value.replace("\n", "\\n").replace("\"", "\\\"")) :
       ValueElement.of(value);
   }