[TINKERPOP-3105] Running 3.6.x python-driver with 3.7.x server leads to deserialization errors

[xiazcy]

Currently, when skipping properties either via tokens or ReferenceElementStrategy with GraphBinaryV1, properties on element will return the default empty list, however drivers of older versions are expecting null properties for Reference Elements, as such serialization errors can occur in GLVs that does strict checking (i.e. python and go).

This PR updated the check to ReferenceVertex/Edge as value.properties() == null won't be reached, and will write null for properties of Reference Elements in the GraphBinary serializer.

Also updated docs to make it more clear.

[kenhuuu]

Did you do the same check for VertexPropertySerializer or are metaproperties expected to be empty list instead of null.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 76.74%. Comparing base (9b46b67) to head (84e31b9).
Report is 203 commits behind head on 3.7-dev.

Files with missing lines	Patch %	Lines
...mlin/structure/io/binary/types/EdgeSerializer.java	0.00%	0 Missing and 1 partial ⚠️
...ture/io/binary/types/VertexPropertySerializer.java	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             3.7-dev    #2742      +/-   ##
=============================================
+ Coverage      76.14%   76.74%   +0.59%     
- Complexity     13152    13204      +52     
=============================================
  Files           1084     1087       +3     
  Lines          65160    66436    +1276     
  Branches        7285     7309      +24     
=============================================
+ Hits           49616    50984    +1368     
+ Misses         12839    12743      -96     
- Partials        2705     2709       +4     

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[xiazcy]

Did you do the same check for VertexPropertySerializer or are metaproperties expected to be empty list instead of null.

Yes, that's now also updated to write null instead of empty list as expected by older drivers.

[spmallette]

Does GraphSON have these problems with 3.6.x drivers connecting to 3.7x servers?

[vkagamlyk]

VOTE+1

[xiazcy]

Does GraphSON have these problems with 3.6.x drivers connecting to 3.7x servers?

No, GraphSON works fine, I've only seen errors in GraphBinary when I tested them. I'll update the docs to specify that.

[Cole-Greer]

VOTE +1