add default value() method for HugeGraphOutput

[javeme]

No description provided.

[codecov]

Codecov Report

Merging #144 (c5a1e6c) into master (74dff02) will decrease coverage by 0.55%.
The diff coverage is 91.66%.

@@ Coverage Diff @@ ## master #144 +/- ## ============================================ - Coverage 87.89% 87.33% -0.56%  + Complexity 2918 2905 -13  ============================================ Files 307 308 +1 Lines 10971 10977 +6 Branches 929 929 ============================================ - Hits 9643 9587 -56  - Misses 882 950 +68  + Partials 446 440 -6 

Impacted Files	Coverage Δ
.../algorithm/centrality/pagerank/PageRankOutput.java	100.00% <ø> (ø)
...m/community/trianglecount/TriangleCountOutput.java	100.00% <ø> (ø)
...ter/algorithm/path/rings/RingsDetectionOutput.java	100.00% <ø> (ø)
...hm/community/trianglecount/TriangleCountValue.java	92.59% <66.66%> (+3.70%)	⬆️
...ithm/centrality/degree/DegreeCentralityOutput.java	100.00% <100.00%> (ø)
...ithm/centrality/degree/DegreeCentralityParams.java	100.00% <100.00%> (ø)
...graph/computer/core/output/hg/HugeGraphOutput.java	96.42% <100.00%> (+0.13%)	⬆️
...ugegraph/computer/core/output/hdfs/HdfsOutput.java	0.00% <0.00%> (-79.63%)	⬇️
...ph/computer/core/output/hdfs/HdfsOutputMerger.java	0.00% <0.00%> (-75.76%)	⬇️
...k8s/operator/controller/ComputerJobController.java	90.94% <0.00%> (+1.44%)	⬆️
... and 1 more

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[javeme]

accidental ci failure:

Error: Tests run: 542, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 212.667 s <<< FAILURE! - in com.baidu.hugegraph.computer.suite.unit.UnitTestSuite Error: testHandlerException(com.baidu.hugegraph.computer.core.network.netty.NettyTransportClientTest) Time elapsed: 0.055 s <<< FAILURE! java.lang.AssertionError: No exception was thrown(expected com.baidu.hugegraph.computer.core.common.exception.TransportException) at com.baidu.hugegraph.computer.core.network.netty.NettyTransportClientTest.testHandlerException(NettyTransportClientTest.java:333)