Set etag to be null if it's empty

[arghya88]

Signed-off-by: Arghya Sadhu arghya88@gmail.com

Description

Convert empty string to null for GRPC implementation to keep it consistent with HTTP implementation

Issue reference

Fixes #405

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[mukundansundar]

lgtm.
@artursouza The issue linked to this should be a breaking change since the response is changing.

[artursouza]

Yes, LGTM. Let's mark it as breaking change - even though it is minor.

[arghya88]

@artursouza I debugged why saveAndGetBulkState test in AbstractStateClientIT is failing. It turns out

1. For the second state object both GRPC and HTTP client returns 1 for Etag even though we set null in the object.
2. For the third object where we don't even save it in state store HTTP client returns empty and GRPC client returns null for Etag.

I am not sure if 1 is expected to be this way. If this is expected then we can keep it this way and let the test pass.
For 2 the tests used to pass before my change because GRPC client used to return empty before my change. With my change it returns null instead of empty and hence test for GRPC client is failing.

2 is not happening in unit tests because units tests don't cover a scenario of trying to retrieve a state object which is not saved at all.

[codecov]

Codecov Report

Merging #414 (7c437ad) into master (7f1ce0b) will decrease coverage by 0.03%.
The diff coverage is 66.66%.

@@             Coverage Diff              @@
##             master     #414      +/-   ##
============================================
- Coverage     83.27%   83.23%   -0.04%     
- Complexity      835      838       +3     
============================================
  Files            72       72              
  Lines          2487     2493       +6     
  Branches        255      258       +3     
============================================
+ Hits           2071     2075       +4     
- Misses          293      294       +1     
- Partials        123      124       +1     

Impacted Files	Coverage Δ	Complexity Δ
...k/src/main/java/io/dapr/client/DaprClientHttp.java	92.80% <0.00%> (-0.71%)	80.00 <0.00> (ø)
...k/src/main/java/io/dapr/client/DaprClientGrpc.java	85.81% <100.00%> (+0.19%)	86.00 <0.00> (+2.00)

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[arghya88]

@artursouza Pls review

[artursouza]

@artursouza I debugged why saveAndGetBulkState test in AbstractStateClientIT is failing. It turns out

1. For the second state object both GRPC and HTTP client returns 1 for Etag even though we set null in the object.
2. For the third object where we don't even save it in state store HTTP client returns empty and GRPC client returns null for Etag.

I am not sure if 1 is expected to be this way. If this is expected then we can keep it this way and let the test pass.
For 2 the tests used to pass before my change because GRPC client used to return empty before my change. With my change it returns null instead of empty and hence test for GRPC client is failing.

2 is not happening in unit tests because units tests don't cover a scenario of trying to retrieve a state object which is not saved at all.

The reason why the etag is "1" and not null even when we set it to null is because Dapr maps etag to version in Redis. Version is always present in Redis, so it defaults to "1" when we set a value: https://github.com/dapr/components-contrib/blob/master/state/redis/redis.go

This is why the integration tests asserts "1" for the null case.