func isMapOfStringToRefOfCommit(m types.Map) bool {
	mapTypes := m.Type().Desc.(types.CompoundDesc).ElemTypes
	keyType, valType := mapTypes[0], mapTypes[1]
	return keyType.Kind() == types.StringKind && (isRefOfCommitType(valType) || isUnionOfRefOfCommitType(valType))
}