MockTaskSideInputHandlerBuilder addStore(String storeName, Set<SystemStreamPartition> storeSSPs) {
      storeToSSPs.put(storeName, storeSSPs);
      storeToProcessor.put(storeName, mock(SideInputsProcessor.class));
      return this;
    }
This test is for cases, when calls to systemAdmin (e.g., KafkaSystemAdmin's) get-stream-metadata method return null.
samza-core/src/test/java/org/apache/samza/storage/TestTaskSideInputHandler.java