Forgetting the argument (or not using = to separate the option from
the argument) resulted in lzma_str_to_filters() being called with NULL
as input string argument. The function handles it fine but xz passes
the NULL to printf() too:
$ xz --filters
xz: Error in --filters=FILTERS option:
xz: (null)
xz: ^
xz: Unexpected NULL pointer argument(s) to lzma_str_to_filters()
Now it's correct:
$ xz --filters
xz: option '--filters' requires an argument
The --filters-help option doesn't take any arguments.