code: private boolean checkForMapKey(TabularType pType) {
          List<String> indexNames = pType.getIndexNames();
          return
                  // Single index named "key"
                  indexNames.size() == 1 && indexNames.contains(TD_KEY_KEY) &&
                  // Only convert to map for simple types for all others use normal conversion. See #105 for details.
                  pType.getRowType().getType(TD_KEY_KEY) instanceof SimpleType;
      }
docs: The tabular data representing a map must have a single index named "key" which must be a simple type