Filter out null, empty and blank elements when mapping feed-scoped ids

[vpaturet]

Summary

As detailed in #5398, specifying a null id in the list of whitelisted lines for estimated calls causes an exception.
Null values should not be allowed as input parameters in this case.

This PR provides a general fix by filtering out null, empty and blank values when mapping ids to feed-scoped ids.

Issue

Closes #5398

Unit tests

Added unit tests

Documentation

No

[codecov]

Codecov Report

Attention: 16 lines in your changes are missing coverage. Please review.

Comparison is base (dcc4037) 66.58% compared to head (dedbd23) 66.59%.

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #5428      +/-   ##
=============================================
+ Coverage      66.58%   66.59%   +0.01%     
- Complexity     15317    15321       +4     
=============================================
  Files           1792     1792              
  Lines          69538    69534       -4     
  Branches        7333     7332       -1     
=============================================
+ Hits           46299    46307       +8     
+ Misses         20756    20746      -10     
+ Partials        2483     2481       -2     

Files	Coverage Δ
...ner/ext/transmodelapi/mapping/TransitIdMapper.java	71.87% <100.00%> (+23.22%)	⬆️
...ner/ext/transmodelapi/TransmodelGraphQLSchema.java	66.84% <0.00%> (ø)
...ext/transmodelapi/mapping/SelectRequestMapper.java	0.00% <0.00%> (ø)
...t/transmodelapi/model/plan/JourneyWhiteListed.java	32.14% <0.00%> (-1.20%)	⬇️
...lanner/ext/transmodelapi/mapping/FilterMapper.java	2.73% <0.00%> (ø)
...r/ext/transmodelapi/mapping/TripRequestMapper.java	56.60% <0.00%> (ø)

... and 2 files with indirect coverage changes

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