code: func (grm *nestedPendingOperations) isOperationExists(
  	volumeName v1.UniqueVolumeName,
  	podName types.UniquePodName) (bool, int) {
  
  	// If volumeName is empty, operation can be executed concurrently
  	if volumeName == EmptyUniqueVolumeName {
  		return false, -1
  	}
  
  	for previousOpIndex, previousOp := range grm.operations {
  		if previousOp.volumeName != volumeName {
  			// No match, keep searching
  			continue
  		}
  
  		if previousOp.podName != EmptyUniquePodName &&
  			podName != EmptyUniquePodName &&
  			previousOp.podName != podName {
  			// No match, keep searching
  			continue
  		}
  
  		// Match
  		return true, previousOpIndex
  	}
  	return false, -1
  }
docs: // This is an internal function and caller should acquire and release the lock