fix task result with path/tree can't be serialized

[javeme]

fix #1331

Change-Id: Ic2c511ad9985f2f83dde8123d2fe149f85cd95bb

[codecov]

Codecov Report

Merging #1351 (8769966) into master (36c58b8) will increase coverage by 0.16%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #1351      +/-   ##
============================================
+ Coverage     62.30%   62.46%   +0.16%     
- Complexity     5799     5815      +16     
============================================
  Files           379      379              
  Lines         31664    31771     +107     
  Branches       4435     4447      +12     
============================================
+ Hits          19729    19847     +118     
+ Misses         9930     9907      -23     
- Partials       2005     2017      +12     

Impacted Files	Coverage Δ	Complexity Δ
...ava/com/baidu/hugegraph/io/HugeGraphSONModule.java	80.18% <100.00%> (+2.51%)	11.00 <1.00> (ø)
.../hugegraph/backend/serializer/TableSerializer.java	86.03% <0.00%> (-1.44%)	61.00% <0.00%> (+3.00%)	⬇️
...a/com/baidu/hugegraph/backend/query/Condition.java	78.10% <0.00%> (-0.37%)	32.00% <0.00%> (ø%)
...hugegraph/backend/serializer/BinarySerializer.java	84.84% <0.00%> (-0.21%)	116.00% <0.00%> (ø%)
...ain/java/com/baidu/hugegraph/api/auth/UserAPI.java	0.00% <0.00%> (ø)	0.00% <0.00%> (ø%)
...in/java/com/baidu/hugegraph/api/auth/GroupAPI.java	0.00% <0.00%> (ø)	0.00% <0.00%> (ø%)
...n/java/com/baidu/hugegraph/api/auth/AccessAPI.java	0.00% <0.00%> (ø)	0.00% <0.00%> (ø%)
...n/java/com/baidu/hugegraph/api/auth/BelongAPI.java	0.00% <0.00%> (ø)	0.00% <0.00%> (ø%)
...n/java/com/baidu/hugegraph/api/auth/TargetAPI.java	0.00% <0.00%> (ø)	0.00% <0.00%> (ø%)
...aidu/hugegraph/schema/builder/AbstractBuilder.java	89.28% <0.00%> (ø)	13.00% <0.00%> (ø%)
... and 11 more

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