## What is the purpose of the change fix issue #2233
## Brief changelog fix the referenceconfig cache null forever if no provider and then provider startup ## Verifying this change 1. provider not startup 2. invoke with reference cache get null 3. provider startup 4. invoker with reference cache again get what you want Follow this checklist to help us incorporate your contribution quickly and easily: - [x] Make sure there is a [GITHUB_issue](https://github.com/apache/incubator-dubbo/issues) filed for the change (usually before you start working on it). Trivial changes like typos do not require a GITHUB issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue. - [x] Format the pull request title like `[Dubbo-XXX] Fix UnknownException when host config not exist #XXX`. Each commit in the pull request should have a meaningful subject line and body. - [x] Write a pull request description that is detailed enough to understand what the pull request does, how, and why. - [x] Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add integration-test in [test module](https://github.com/apache/incubator-dubbo/tree/master/dubbo-test). - [x] Run `mvn clean install -DskipTests` & `mvn clean test-compile failsafe:integration-test` to make sure unit-test and integration-test pass. - [x] If this contribution is large, please follow the [Software Donation Guide](https://github.com/apache/incubator-dubbo/wiki/Software-donation-guide). [ Full content available at: https://github.com/apache/incubator-dubbo/pull/2347 ] This message was relayed via gitbox.apache.org for [email protected]
