ShardingSphere分库分表schema名称导致NPE问题排查记录

前段时间把 ShardingSphere 升级到了 5.1.1 版本，奈何官方版本升级太快跟不上速度，这不近又发现了一个 BUG。

问题现象

数据库做了分库分表，在需要查询多表数据进行 merge 的时候发生了一个 NPE 的异常。

Caused by: java.lang.NullPointerException    at org.apache.shardingsphere.sharding.merge.dql.orderby.OrderByValue.getOrderValuesCaseSensitiveFromTables(OrderByValue.java:73) ~[shardingsphere-sharding-core-5.1.1.jar:5.1.1]    at org.apache.shardingsphere.sharding.merge.dql.orderby.OrderByValue.getOrderValuesCaseSensitive(OrderByValue.java:64) ~[shardingsphere-sharding-core-5.1.1.jar:5.1.1]    at org.apache.shardingsphere.sharding.merge.dql.orderby.OrderByValue.(OrderByValue.java:58) ~[shardingsphere-sharding-core-5.1.1.jar:5.1.1]    at org.apache.shardingsphere.sharding.merge.dql.orderby.OrderByStreamMergedResult.orderResultSetsToQueue(OrderByStreamMergedResult.java:56) ~[shardingsphere-sharding-core-5.1.1.jar:5.1.1]    at org.apache.shardingsphere.sharding.merge.dql.orderby.OrderByStreamMergedResult.(OrderByStreamMergedResult.java:50) ~[shardingsphere-sharding-core-5.1.1.jar:5.1.1]    at org.apache.shardingsphere.sharding.merge.dql.ShardingDQLResultMerger.build(ShardingDQLResultMerger.java:89) ~[shardingsphere-sharding-core-5.1.1.jar:5.1.1]    at org.apache.shardingsphere.sharding.merge.dql.ShardingDQLResultMerger.merge(ShardingDQLResultMerger.java:63) ~[shardingsphere-sharding-core-5.1.1.jar:5.1.1]    at org.apache.shardingsphere.infra.merge.MergeEngine.executeMerge(MergeEngine.java:90) ~[shardingsphere-infra-merge-5.1.1.jar:5.1.1]    at org.apache.shardingsphere.infra.merge.MergeEngine.merge(MergeEngine.java:80) ~[shardingsphere-infra-merge-5.1.1.jar:5.1.1]    at org.apache.shardingsphere.driver.jdbc.core.statement.ShardingSpherePreparedStatement.mergeQuery(ShardingSpherePreparedStatement.java:487) ~[shardingsphere-jdbc-core-5.1.1.jar:5.1.1]    at org.apache.shardingsphere.driver.jdbc.core.statement.ShardingSpherePreparedStatement.getResultSet(ShardingSpherePreparedStatement.java:435) ~[shardingsphere-jdbc-core-5.1.1.jar:5.1.1]    at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.getFirstResultSet(DefaultResultSetHandler.java:237) ~[mybatis-3.5.3.jar:3.5.3]    at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSets(DefaultResultSetHandler.java:187) ~[mybatis-3.5.3.jar:3.5.3]    at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:65) ~[mybatis-3.5.3.jar:3.5.3]    at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79) ~[mybatis-3.5.3.jar:3.5.3]    at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:63) ~[mybatis-3.5.3.jar:3.5.3]    at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324) ~[mybatis-3.5.3.jar:3.5.3]    at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156) ~[mybatis-3.5.3.jar:3.5.3]    at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109) ~[mybatis-3.5.3.jar:3.5.3]    at jdk.internal.reflect.GeneratedMethodAccessor346.invoke(Unknown Source) ~[?:?]    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]    at java.lang.reflect.Method.invoke(Method.java:566) ~[?:?]    at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:63) ~[mybatis-3.5.3.jar:3.5.3]    at com.sun.proxy.$Proxy410.query(Unknown Source) ~[?:?]    at com.github.pagehelper.PageInterceptor.intercept(PageInterceptor.java:108) ~[pagehelper-5.1.11.jar:?]    at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61) ~[mybatis-3.5.3.jar:3.5.3]    at com.sun.proxy.$Proxy410.query(Unknown Source) ~[?:?]    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:147) ~[mybatis-3.5.3.jar:3.5.3]    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:140) ~[mybatis-3.5.3.jar:3.5.3]    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]    at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:?]    at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]    at java.lang.reflect.Method.invoke(Method.java:566) ~[?:?]    at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:427) ~[mybatis-spring-2.0.6.jar:2.0.6]    ... 95 more 问题排查