code: public void updateMasterPropertyMetadataMap(String mappedName, String qualifiedName) {
      String old = masterPropertyMetadataMap.put(mappedName, qualifiedName);
      if (old != null) {
        String message = "Duplicate property %s in entity %s. Check fields %s and %s";
        throw new EntityManagerException(
            String.format(message, mappedName, entityClass.getName(), old, qualifiedName));
      }
  
    }
docs: Updates the master property metadata map with the given property metadata.
  
  @param mappedName
  the mapped name (or property name in the datastore)
  @param qualifiedName
  the qualified name of the field
  
  @throws EntityManagerException
  if a property with the same mapped name already exists.