Warning from systools:make_relup/4 crashes relx

If systools:make_relup/4 returns {ok, Relup, Module, Warnings}, where Warnings=/=[], then relx crashes with function_clause in rlx_prv_relup:format_error/1, since it does not handle the tag relup_script_generation_warn.

Apart from the bug, what is the reasoning behind failing the relup generation due to warnings? Could it be considered to allow the warnings_as_errors option here, and only fail if this is set?