-P/--no-pigz option always fails because of incorrect conditional expression
-P/--no-pigz option always fails because of incorrect conditional expression

Bash conditional expression should test for non-zero pigz variable (-n) instead for zero variable (-z) at line 80.  See: https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html#Bash-Conditional-Expressions

Thanks for all the work.  Love this set of utilities.
binwiederhier/zfsu