PowerFlex: REST API call fails with incomplete response

Some REST API calls (such as "/api/instances") fail with incomplete response. For example:

...vtreeMigrationInfo":{"sourceStoragePoolId":"<storage_pool_id>","destinationStoragePoolId":{"message":"ERROR","httpStatusCode":500,"errorCode":0}

But localhost_access log reports a successful request (status 200):

<client ip> - - [12/Jun/2020:13:23:01 +0000] "GET /api/instances HTTP/1.1" 200 106376

While scaleio-trace.log contains the following Exception:

2020-06-12 13:23:01,377 [https-jsse-nio-443-exec-8] DEBUG o.s.w.s.m.m.a.ExceptionHandlerExceptionResolver - Resolving exception from handler [public java.lang.Object com.emc.s3g.scaleio.web.controller.SpecialImplController.getAllInstances(javax.servlet.http.HttpServletRequest) throws com.emc.s3g.scaleio.common.gateway.ScaleIOException]: org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: (was java.lang.NullPointerException) (through reference chain: java.util.HashMap["vTreeList"]->java.util.ArrayList[74]->com.emc.s3g.scaleio.repository.entity.wrappers.VTreeWrapper["rootVolumes"]); nested exception is org.codehaus.jackson.map.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: java.util.HashMap["vTreeList"]->java.util.ArrayList[74]->com.emc.s3g.scaleio.repository.entity.wrappers.VTreeWrapper["rootVolumes"])
2020-06-12 13:23:01,377 [https-jsse-nio-443-exec-8] DEBUG o.s.w.s.m.m.a.ExceptionHandlerExceptionResolver - Invoking @ExceptionHandler method: public com.emc.s3g.scaleio.web.entity.Result com.emc.s3g.scaleio.web.controller.BaseController.handleException(java.lang.Exception,javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2020-06-12 13:23:01,389 [https-jsse-nio-443-exec-8] ERROR c.e.s.s.w.c.SpecialImplController - Got an exception in handleException
org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: (was java.lang.NullPointerException) (through reference chain: java.util.HashMap["vTreeList"]->java.util.ArrayList[74]->com.emc.s3g.scaleio.repos
itory.entity.wrappers.VTreeWrapper["rootVolumes"]); nested exception is org.codehaus.jackson.map.JsonMappingException: (was java.lang.NullPointerException

Scenario

There were volume deletions shortly before the REST API call was made.

Impact

REST API query failures

The volume deletion takes time and not all data structures are removed simultaneously. This may cause the REST API server to fail to generate a response to some REST API calls.

Try again later.
After the background process for volume deletion has completed, the same REST API call should succeed.

Impacted Versions

3.0.x
3.0.1.x