There are still changes to commit

```
2019-09-26 19:34:15 199000 [task-worker-1] [WARN ] com.baidu.hugegraph.task.HugeTask [] - An exception occurred when running task: 5
com.baidu.hugegraph.HugeException: Failed to remove vertices
at com.baidu.hugegraph.backend.tx.GraphTransaction.removeVertices(GraphTransaction.java:1434) ~[classes/:?]
at com.baidu.hugegraph.job.schema.VertexLabelRemoveCallable.removeVertexLabel(VertexLabelRemoveCallable.java:83) ~[classes/:?]
at com.baidu.hugegraph.job.schema.VertexLabelRemoveCallable.execute(VertexLabelRemoveCallable.java:45) ~[classes/:?]
at com.baidu.hugegraph.job.Job.call(Job.java:40) ~[classes/:?]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_111]
at com.baidu.hugegraph.task.HugeTask.run(HugeTask.java:203) [classes/:?]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_111]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_111]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [?:1.8.0_111]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [?:1.8.0_111]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_111]
Caused by: java.lang.IllegalArgumentException: Undefined edge label with id: '7'
at com.google.common.base.Preconditions.checkArgument(Preconditions.java:146) ~[guava-19.0.jar:?]
at com.baidu.hugegraph.util.E.checkArgument(E.java:56) ~[hugegraph-common-1.6.14.jar:1.6.14.0]
at com.baidu.hugegraph.HugeGraph.edgeLabel(HugeGraph.java:460) ~[classes/:?]
at com.baidu.hugegraph.backend.serializer.BinarySerializer.parseEdge(BinarySerializer.java:256) ~[classes/:?]
at com.baidu.hugegraph.backend.serializer.BinarySerializer.parseColumn(BinarySerializer.java:307) ~[classes/:?]
at com.baidu.hugegraph.backend.serializer.BinarySerializer.readVertex(BinarySerializer.java:409) ~[classes/:?]
at com.baidu.hugegraph.backend.tx.GraphTransaction.lambda$queryEdgesFromBackend$6(GraphTransaction.java:756) ~[classes/:?]
at com.baidu.hugegraph.iterator.FlatMapperIterator.fetch(FlatMapperIterator.java:55) ~[hugegraph-common-1.6.14.jar:1.6.14.0]
at com.baidu.hugegraph.iterator.WrappedIterator.hasNext(WrappedIterator.java:41) ~[hugegraph-common-1.6.14.jar:1.6.14.0]
at com.google.common.collect.ImmutableList.copyOf(ImmutableList.java:249) ~[guava-19.0.jar:?]
at com.baidu.hugegraph.backend.cache.CachedGraphTransaction.queryEdgesFromBackend(CachedGraphTransaction.java:192) ~[classes/:?]
at com.baidu.hugegraph.backend.tx.GraphTransaction.prepareDeletions(GraphTransaction.java:266) ~[classes/:?]
at com.baidu.hugegraph.backend.tx.GraphTransaction.prepareCommit(GraphTransaction.java:212) ~[classes/:?]
at com.baidu.hugegraph.backend.tx.IndexableTransaction.commit2Backend(IndexableTransaction.java:53) ~[classes/:?]
at com.baidu.hugegraph.backend.tx.AbstractTransaction.commit(AbstractTransaction.java:168) ~[classes/:?]
at com.baidu.hugegraph.backend.tx.GraphTransaction.commit(GraphTransaction.java:364) ~[classes/:?]
at com.baidu.hugegraph.backend.tx.GraphTransaction.removeVertices(GraphTransaction.java:1431) ~[classes/:?]
... 10 more
2019-09-26 19:34:16 199637 [task-worker-4] [WARN ] com.baidu.hugegraph.task.HugeTask [] - An exception occurred when running task: 7
com.baidu.hugegraph.backend.BackendException: There are still changes to commit
at com.baidu.hugegraph.backend.tx.GraphTransaction.removeEdges(GraphTransaction.java:1442) ~[classes/:?]
at com.baidu.hugegraph.job.schema.EdgeLabelRemoveCallable.removeEdgeLabel(EdgeLabelRemoveCallable.java:65) ~[classes/:?]
at com.baidu.hugegraph.job.schema.EdgeLabelRemoveCallable.execute(EdgeLabelRemoveCallable.java:42) ~[classes/:?]
at com.baidu.hugegraph.job.Job.call(Job.java:40) ~[classes/:?]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_111]
at com.baidu.hugegraph.task.HugeTask.run(HugeTask.java:203) [classes/:?]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_111]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_111]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [?:1.8.0_111]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [?:1.8.0_111]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_111]
```

Another error:
```
2019-09-26 20:32:50 330470 [task-worker-1] [WARN ] com.baidu.hugegraph.task.HugeTask [] - An exception occurred when running task: 195
java.lang.AssertionError: null
at com.baidu.hugegraph.backend.store.rocksdb.RocksDBStdSessions$StdSession.scan(RocksDBStdSessions.java:651) ~[classes/:?]
at com.baidu.hugegraph.backend.store.rocksdb.RocksDBTable.queryByPrefix(RocksDBTable.java:173) ~[classes/:?]
at com.baidu.hugegraph.backend.store.rocksdb.RocksDBTable.query(RocksDBTable.java:129) ~[classes/:?]
at com.baidu.hugegraph.backend.store.rocksdb.RocksDBStore.query(RocksDBStore.java:320) ~[classes/:?]
at com.baidu.hugegraph.backend.tx.AbstractTransaction.query(AbstractTransaction.java:105) ~[classes/:?]
at com.baidu.hugegraph.backend.tx.GraphIndexTransaction.doIndexQueryOnce(GraphIndexTransaction.java:513) ~[classes/:?]
at com.baidu.hugegraph.backend.tx.GraphIndexTransaction.lambda$doIndexQuery$0(GraphIndexTransaction.java:499) ~[classes/:?]
at com.baidu.hugegraph.backend.page.IdHolder.fetchNext(IdHolder.java:98) ~[classes/:?]
at com.baidu.hugegraph.backend.page.QueryList$IndexQuery.iterator(QueryList.java:250) ~[classes/:?]
at com.baidu.hugegraph.backend.page.QueryList.fetchNext(QueryList.java:124) ~[classes/:?]
at com.baidu.hugegraph.backend.page.PageEntryIterator.fetch(PageEntryIterator.java:79) ~[classes/:?]
at com.baidu.hugegraph.backend.page.PageEntryIterator.hasNext(PageEntryIterator.java:66) ~[classes/:?]
at com.baidu.hugegraph.iterator.FlatMapperIterator.fetch(FlatMapperIterator.java:52) ~[hugegraph-common-1.6.14.jar:1.6.14.0]
at com.baidu.hugegraph.iterator.WrappedIterator.hasNext(WrappedIterator.java:41) ~[hugegraph-common-1.6.14.jar:1.6.14.0]
at com.baidu.hugegraph.iterator.FilterIterator.fetch(FilterIterator.java:42) ~[hugegraph-common-1.6.14.jar:1.6.14.0]
at com.baidu.hugegraph.iterator.WrappedIterator.hasNext(WrappedIterator.java:41) ~[hugegraph-common-1.6.14.jar:1.6.14.0]
at com.baidu.hugegraph.backend.tx.GraphTransaction.traverseByLabel(GraphTransaction.java:1504) ~[classes/:?]
at com.baidu.hugegraph.backend.tx.GraphTransaction.traverseEdgesByLabel(GraphTransaction.java:1479) ~[classes/:?]
at com.baidu.hugegraph.backend.tx.GraphTransaction.removeEdges(GraphTransaction.java:1457) ~[classes/:?]
at com.baidu.hugegraph.job.schema.EdgeLabelRemoveCallable.removeEdgeLabel(EdgeLabelRemoveCallable.java:65) ~[classes/:?]
at com.baidu.hugegraph.job.schema.EdgeLabelRemoveCallable.execute(EdgeLabelRemoveCallable.java:42) ~[classes/:?]
at com.baidu.hugegraph.job.Job.call(Job.java:40) ~[classes/:?]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_111]
at com.baidu.hugegraph.task.HugeTask.run(HugeTask.java:203) [classes/:?]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_111]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_111]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [?:1.8.0_111]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [?:1.8.0_111]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_111]
```