nifgen system tests don't exercise TypeError throw cases when creating waveforms with numpy

[tdunkle]

Description of issue

The nifgen system-level tests suite doesn't include tests that exercise the TypeError throw cases when creating waveforms with numpy. This was pointed out by @marcoskirsch here: c64c983#r1013088620

System report

None.

Steps to reproduce issue

Run the system level tests. Try commenting out the TypeError throws in this block, and note that all of the tests still pass.