code: public static Pair<String, String> splitColumnName(String columnName)
    {
      final int i = columnName.indexOf('.');
      if (i < 0) {
        return Pair.of(columnName, null);
      } else {
        return Pair.of(columnName.substring(0, i), columnName.substring(i + 1));
      }
    }
docs: Split a dot-style columnName into the "main" columnName and the subColumn name after the dot. Useful for
  columns that support dot notation.
  
  @param columnName columnName like "foo" or "foo.bar"
  
  @return pair of main column name (will not be null) and subColumn name (may be null)