Intent of nil_payloads_are_filtered

All 3 exact tests in this concept. Every test is marked by where it enters the hierarchy.

go.temporal.io/ 3 tests
- server/ 3 tests
  - common/ 3 tests
    
    payload/ 3 tests
    
    TestMergeMapOfPayload/ 1 test
    
    go.temporal.io/server/common/payload/TestMergeMapOfPayload/nil_payloads_are_filtered Introduced here
    
    go.temporal.io/server/common/payload/TestFilterNilMemo Inherited payload.go ×1
    
    go.temporal.io/server/common/payload/TestFilterNilSearchAttributes Inherited TestFilterNilSearchAttributes