For the `com_item_missingness` function, the error message on ill-formatted missing tables in argument `cause_label_df` is quite confusing: ```r replacement has 0 rows, data has 138 ``` The missing table should be verified regarding its column names and types for being valid. Also, a duplicate check should be amended. Later, the table could be extended by another column referring variable names -- if given, we could have the same missing code with different meanings for different variables.