Parse NeTEx Resource frame without organisation

[vpaturet]

Summary

In the Nordic NeTEx Profile, organisations are optional elements in the ResourceFrame.
Currently the graph builder fails with a NullPointerException if a ResourceFrame does not contain any organisations:

An uncaught error occurred inside OTP: java.lang.NullPointerException: Cannot invoke "org.rutebanken.netex.model.OrganisationsInFrame_RelStructure.getOrganisation_()" because "elements" is null
java.lang.RuntimeException: java.lang.NullPointerException: Cannot invoke "org.rutebanken.netex.model.OrganisationsInFrame_RelStructure.getOrganisation_()" because "elements" is null
	at org.opentripplanner.netex.NetexModule.buildGraph(NetexModule.java:107)
	at org.opentripplanner.graph_builder.GraphBuilder.run(GraphBuilder.java:175)
	at org.opentripplanner.standalone.OTPMain.startOTPServer(OTPMain.java:141)
	at org.opentripplanner.standalone.OTPMain.main(OTPMain.java:55)
Caused by: java.lang.NullPointerException: Cannot invoke "org.rutebanken.netex.model.OrganisationsInFrame_RelStructure.getOrganisation_()" because "elements" is null
	at org.opentripplanner.netex.loader.parser.ResourceFrameParser.parseOrganization(ResourceFrameParser.java:60)
	at org.opentripplanner.netex.loader.parser.ResourceFrameParser.parse(ResourceFrameParser.java:27)
	at org.opentripplanner.netex.loader.parser.ResourceFrameParser.parse(ResourceFrameParser.java:17)
	at org.opentripplanner.netex.loader.parser.NetexDocumentParser.parse(NetexDocumentParser.java:107)
	at org.opentripplanner.netex.loader.parser.NetexDocumentParser.parseCommonFrame(NetexDocumentParser.java:69)
	at org.opentripplanner.netex.loader.parser.NetexDocumentParser.parseFrameList(NetexDocumentParser.java:63)
	at org.opentripplanner.netex.loader.parser.NetexDocumentParser.parse(NetexDocumentParser.java:58)
	at org.opentripplanner.netex.loader.parser.NetexDocumentParser.parseAndPopulateIndex(NetexDocumentParser.java:49)
	at org.opentripplanner.netex.NetexBundle.loadSingeFileEntry(NetexBundle.java:182)
	at org.opentripplanner.netex.NetexBundle.loadFilesThenMapToOtpTransitModel(NetexBundle.java:166)
	at org.opentripplanner.netex.NetexBundle.loadFileEntries(NetexBundle.java:121)
	at org.opentripplanner.netex.NetexBundle.loadBundle(NetexBundle.java:100)
	at org.opentripplanner.netex.NetexModule.buildGraph(NetexModule.java:66)

This PR ensures that the graph builder can parse a ResourceFrame without organisation.

Issue

No

Unit tests

Added unit test

Documentation

No

[codecov]

Codecov Report

Patch coverage: 87.50% and project coverage change: -0.01% ⚠️

Comparison is base (36edab0) 66.38% compared to head (f26866e) 66.38%.

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #5336      +/-   ##
=============================================
- Coverage      66.38%   66.38%   -0.01%     
- Complexity     15176    15178       +2     
=============================================
  Files           1785     1785              
  Lines          69163    69164       +1     
  Branches        7334     7335       +1     
=============================================
  Hits           45914    45914              
- Misses         20767    20768       +1     
  Partials        2482     2482              

Files Changed	Coverage Δ
...anner/netex/loader/parser/ResourceFrameParser.java	77.55% <87.50%> (+0.46%)	⬆️

... and 3 files with indirect coverage changes

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