Create instance of NullHandler, instead of class reference

[axonxorz]

Fix for #401

[codecov-io]

Codecov Report

Merging #402 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #402   +/-   ##
=======================================
  Coverage   82.45%   82.45%           
=======================================
  Files          23       23           
  Lines        3265     3265           
  Branches      764      764           
=======================================
  Hits         2692     2692           
  Misses        432      432           
  Partials      141      141

Impacted Files	Coverage Δ
pyxform/xform2json.py	79.66% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a619d24...0265402. Read the comment docs.