Fix null property value parsing of search document

[sazzad16]

when it was:

• set from outside Jedis
• not carried by JSONObject
• not serialized by default Gson

[codecov-commenter]

Codecov Report

Base: 66.68% // Head: 66.78% // Increases project coverage by +0.09% 🎉

Coverage data is based on head (752add7) compared to base (899eb05).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3148      +/-   ##
============================================
+ Coverage     66.68%   66.78%   +0.09%     
- Complexity     4495     4502       +7     
============================================
  Files           246      246              
  Lines         14545    14549       +4     
  Branches        887      887              
============================================
+ Hits           9700     9716      +16     
+ Misses         4462     4453       -9     
+ Partials        383      380       -3     

Impacted Files	Coverage Δ
...main/java/redis/clients/jedis/search/Document.java	83.33% <100.00%> (+1.75%)	⬆️
.../java/redis/clients/jedis/search/SearchResult.java	100.00% <100.00%> (ø)
src/main/java/redis/clients/jedis/Protocol.java	91.87% <0.00%> (+1.25%)	⬆️
...ava/redis/clients/jedis/JedisClusterInfoCache.java	74.35% <0.00%> (+1.28%)	⬆️
src/main/java/redis/clients/jedis/JedisPubSub.java	71.81% <0.00%> (+1.81%)	⬆️
...nts/jedis/providers/ClusterConnectionProvider.java	78.18% <0.00%> (+5.45%)	⬆️
...lients/jedis/search/schemafields/NumericField.java	78.94% <0.00%> (+15.78%)	⬆️

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