Is there an existing issue for this?

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Current Behavior

[ERROR] Tests run: 3, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.718 s <<< FAILURE! - in org.apache.shenyu.registry.etcd.EtcdInstanceRegisterRepositoryTest
[ERROR] org.apache.shenyu.registry.etcd.EtcdInstanceRegisterRepositoryTest.testSelectInstancesAndWatcher Time elapsed: 0.479 s <<< ERROR!
java.lang.NullPointerException: Cannot invoke "String.split(String)" because the return value of "org.apache.shenyu.registry.api.config.RegisterConfig.getServerLists()" is null
at org.apache.shenyu.registry.etcd.EtcdInstanceRegisterRepositoryTest.testSelectInstancesAndWatcher(EtcdInstanceRegisterRepositoryTest.java:156)
[INFO] Running org.apache.shenyu.registry.etcd.EtcdClientTest
[INFO] Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.041 s - in org.apache.shenyu.registry.etcd.EtcdClientTest

Expected Behavior

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Steps To Reproduce

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Environment

ShenYu version(s): master

Debug logs

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Anything else?

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