fix: empty label exception should be labelCanNotBeNull()

[seagle-yuan]

fix sub-issue 8 #2058

[codecov]

Codecov Report

Merging #2063 (eb0419f) into master (eb7a65c) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master    #2063      +/-   ##
============================================
- Coverage     68.35%   68.34%   -0.01%     
  Complexity      977      977              
============================================
  Files           481      481              
  Lines         39821    39823       +2     
  Branches       5598     5599       +1     
============================================
  Hits          27219    27219              
- Misses         9957     9959       +2     
  Partials       2645     2645              

Impacted Files	Coverage Δ
...va/org/apache/hugegraph/structure/HugeElement.java	73.30% <0.00%> (-0.67%)	⬇️
.../hugegraph/backend/store/rocksdb/RocksDBTable.java	67.11% <0.00%> (-2.02%)	⬇️
...ugegraph/backend/store/raft/StoreStateMachine.java	64.86% <0.00%> (-0.91%)	⬇️
...a/org/apache/hugegraph/backend/cache/RamCache.java	72.92% <0.00%> (-0.56%)	⬇️
...a/org/apache/hugegraph/util/collection/IntMap.java	72.40% <0.00%> (-0.40%)	⬇️
...hugegraph/backend/store/raft/rpc/RpcForwarder.java	69.49% <0.00%> (ø)
...a/org/apache/hugegraph/util/collection/IntSet.java	75.00% <0.00%> (+1.27%)	⬆️
...gegraph/election/RoleElectionStateMachineImpl.java	70.96% <0.00%> (+2.41%)	⬆️

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[javeme]

ci error

Error:  Failures: 
Error:    AuthTest.testDeleteBelong:867 Bad exception type java.lang.IllegalStateException(expected java.lang.IllegalArgumentException)
Error:    AuthTest.testGetBelong:795 Bad exception type java.lang.IllegalStateException(expected java.lang.IllegalArgumentException)
Error:    VertexCoreTest.testAddVertexWithPrimaryValuesEmpty:841 Bad exception type java.lang.IllegalStateException(expected java.lang.IllegalArgumentException)
Error:  Errors: 
Error:    EdgeCoreTest.testQueryEdgeByPropertyWithEmptyString:6931 » IllegalState The pr...
Error:    VertexCoreTest.testAddVerticesWithUniqueIndexForNullableProperties:5946 » IllegalState
Error:    VertexCoreTest.testQueryVertexByPropertyWithEmptyString:6438 » IllegalState Th...
[INFO] 
Error:  Tests run: 731, Failures: 3, Errors: 3, Skipped: 81