cache: fix assert node.next==empty

[javeme]

Change-Id: Idd337f2bebff2b03a5eefdfb9b189b9e012a7ae2

[codecov]

Codecov Report

Merging #1790 (0f7cef0) into master (730f332) will increase coverage by 3.97%.
The diff coverage is 25.00%.

@@             Coverage Diff              @@
##             master    #1790      +/-   ##
============================================
+ Coverage     66.85%   70.83%   +3.97%     
- Complexity      972      978       +6     
============================================
  Files           443      446       +3     
  Lines         37738    37782      +44     
  Branches       5381     5381              
============================================
+ Hits          25229    26762    +1533     
+ Misses         9788     8297    -1491     
- Partials       2721     2723       +2     

Impacted Files	Coverage Δ
...va/com/baidu/hugegraph/backend/cache/RamCache.java	72.06% <25.00%> (+0.15%)	⬆️
.../baidu/hugegraph/security/HugeSecurityManager.java	78.74% <0.00%> (-1.76%)	⬇️
...va/com/baidu/hugegraph/util/collection/IntSet.java	73.61% <0.00%> (-1.28%)	⬇️
...in/java/com/baidu/hugegraph/auth/HugeResource.java	78.08% <0.00%> (-0.49%)	⬇️
...om/baidu/hugegraph/backend/store/ram/RamTable.java	66.55% <0.00%> (-0.23%)	⬇️
...ugegraph/backend/serializer/TableBackendEntry.java	88.88% <0.00%> (-0.12%)	⬇️
...hugegraph/backend/serializer/TextBackendEntry.java	83.33% <0.00%> (-0.10%)	⬇️
...n/java/com/baidu/hugegraph/version/ApiVersion.java	75.00% <0.00%> (ø)
...in/java/com/baidu/hugegraph/backend/id/IdUtil.java	86.79% <0.00%> (ø)
.../java/com/baidu/hugegraph/api/graph/VertexAPI.java	35.46% <0.00%> (ø)
... and 124 more

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