Tries to merge two strings.

    The string are required to be the same ignoring case. The second string is
    always used as the merged value.

    Args:
      a: The first string.
      b: The second string.

    Returns:
      The merged string. This is equal to the second string.

    Raises:
      MergeError: The strings were not the same ignoring case.

def _MergeIdenticalCaseInsensitive(self, a, b):
    """Tries to merge two strings.

    The string are required to be the same ignoring case. The second string is
    always used as the merged value.

    Args:
      a: The first string.
      b: The second string.

    Returns:
      The merged string. This is equal to the second string.

    Raises:
      MergeError: The strings were not the same ignoring case.
    """
    if a.lower() != b.lower():
      raise MergeError("values must be the same (case insensitive) "
                       "('%s' vs '%s')" % (transitfeed.EncodeUnicode(a),
                                           transitfeed.EncodeUnicode(b)))
    return b