class_docstr: Raised when input data cannot be merged into a variable font.
code: def offender(self):
      if "expected" in self.cause and "got" in self.cause:
          index = [
              x == self.cause["expected"] for x in self.cause["got"]
          ].index(False)
          master_name = self._master_name(index)
          if "location" in self.cause:
              master_name = f"{master_name} ({self.cause['location']})"
          return index, master_name
      return None, None
  
imports: import textwrap
label_desc: Use image node_id 4 for calling the VarLibMergeError obj's underlying member method code with example usage: obj.offender() and returns: None,  None, index,  master_name