fix schema validation prohibiting job execution with empty string input

[fmigneault]

Fixes

• Fix Job creation failing when submitting an empty string as input for a Process that allows it due to schema validation incorrectly preventing it.

[codecov[bot]]

Codecov Report

Merging #554 (97e800c) into master (f7be768) will increase coverage by 0.00%. The diff coverage is 92.30%.

@@           Coverage Diff           @@
##           master     #554   +/-   ##
=======================================
  Coverage   84.43%   84.43%           
=======================================
  Files          79       79           
  Lines       17637    17641    +4     
  Branches     2674     2675    +1     
=======================================
+ Hits        14891    14895    +4     
  Misses       2019     2019           
  Partials      727      727           

Files Changed	Coverage Δ
weaver/utils.py	82.85% <88.88%> (-0.01%)	:arrow_down:
weaver/processes/convert.py	84.07% <100.00%> (+0.05%)	:arrow_up:
weaver/wps_restapi/swagger_definitions.py	99.82% <100.00%> (ø)