It depends on which OS you're on.

GNU xargs: Normally runs the command at least once, but you can turn that off with "-r" or "--no-run-if-empty".

OpenBSD xargs: Like GNU, but only has the short "-r" version of the flag.

FreeBSD xargs: Never runs the command if the input is empty, has "-r" (but not "--no-run-if-empty") as a no-op compatibility flag for GNU.

macOS xargs: Never runs the command if the input is empty (has no "-r" or "--no-run-if-empty" flags).