gh-2483: Added StringSerialiser changes and amended tests

[t92549]

Potentially breaking changes that will need to be tested more and go in Gaffer 2.

Related Issue

• Resolve #2483

[codecov-commenter]

Codecov Report

Merging #2486 (090f066) into develop (7fd5c96) will increase coverage by 0.01%. The diff coverage is 92.30%.

@@              Coverage Diff              @@
##             develop    #2486      +/-   ##
=============================================
+ Coverage      66.92%   66.93%   +0.01%     
- Complexity      2444     2447       +3     
=============================================
  Files            973      973              
  Lines          31909    31920      +11     
  Branches        3883     3887       +4     
=============================================
+ Hits           21355    21366      +11     
  Misses          8886     8886              
  Partials        1668     1668              

Impacted Files	Coverage Δ
...fer/accumulostore/key/impl/AggregatorIterator.java	50.94% <0.00%> (-2.00%)	:arrow_down:
...v/gchq/gaffer/serialisation/ToBytesSerialiser.java	33.33% <100.00%> (+8.33%)	:arrow_up:
...er/serialisation/ToBytesViaStringDeserialiser.java	52.38% <100.00%> (+2.38%)	:arrow_up:
...er/serialisation/implementation/MapSerialiser.java	64.47% <100.00%> (ø)
...serialisation/implementation/StringSerialiser.java	81.81% <100.00%> (+1.81%)	:arrow_up:
.../core/AbstractCoreKeyAccumuloElementConverter.java	84.16% <100.00%> (+0.33%)	:arrow_up:
...hbasestore/serialisation/ElementSerialisation.java	77.19% <100.00%> (+0.06%)	:arrow_up:
...java/uk/gov/gchq/gaffer/mapstore/impl/MapImpl.java	81.65% <100.00%> (ø)
.../gchq/gaffer/jsonserialisation/JSONSerialiser.java	74.31% <0.00%> (+1.83%)	:arrow_up:

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[t92549]

This PR has been put on hold until a decision has been made regarding whether to update all of the Serialisers to differentiate null and empty values. See https://github.com/gchq/Gaffer/pull/2486#discussion_r709438443. If this were to happen, a new issue will be made and it will probably be incorporated into Gaffer v2.

[n3101]

@t92549 For planning purposes - does this depend on any other 2.0 work, or could it be done in parallel if effort becomes available?

[t92549]

This work can be done in isolation from any 2.0 changes.

Development stalled though because we couldn't decide how best to implement these fixes. They could be implemented as a breaking change, or as additional serialisers. We also weren't sure if the fixes that add more consistency were worth potentially increasing data volumes.

More discussion needed before more work is done.

[n3101]

@t92549 "This work can be done in isolation from any 2.0 changes.

Development stalled though because we couldn't decide how best to implement these fixes. They could be implemented as a breaking change, or as additional serialisers. We also weren't sure if the fixes that add more consistency were worth potentially increasing data volumes.

More discussion needed before more work is done."

Ok, for now I have labelled this as post-2.0, BUT if we don't do this in 2.0, then that rules out breaking changes. Lets discuss further.

[t92549]

Closed because this branch should be adapted to provide an alternate serialiser, rather than breaking the existing one

[t92549]

Note the branch will be kept as a reference implementation