Cannot recognize 2.6.x compatible rules from dubbo-admin.

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see issue apache/dubbo-admin#392

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Turns out this is not a real bug.

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https://github.com/apache/incubator-dubbo/blob/cdce2b278364c6391a07e35bca8dd5750529a63e/dubbo-cluster/src/main/java/org/apache/dubbo/rpc/cluster/configurator/AbstractConfigurator.java#L128