code: public static String getColumnSharedPrefixOfAssociatedEntityLink(AssociationKey associationKey) {
  		String[] associationKeyColumns = associationKey.getMetadata()
  				.getAssociatedEntityKeyMetadata()
  				.getAssociationKeyColumns();
  		// we used to check that columns are the same (in an ordered fashion)
  		// but to handle List and Map and store indexes / keys at the same level as the id columns
  		// this check is removed
  		String prefix = DocumentHelpers.getColumnSharedPrefix( associationKeyColumns );
  		return prefix == null ? "" : prefix + ".";
  	}
docs: Returns the shared prefix with a trailing dot (.) of the association columns or {@literal null} if there is no shared prefix.
  
  @param associationKey the association key
  
  @return the shared prefix with a trailing dot (.) of the association columns or {@literal null}