[clang] [clang] explicitly check if ParentMap contains key (PR #121736)

llvmbot wrote: @llvm/pr-subscribers-clang Author: Sameer Sahasrabuddhe (ssahasra) Changes The implementation of ParentMap assumes that the key is absent if it is mapped to nullptr. This breaks when trying to store a tuple as the value type. Remove this assumption by explicit uses of `con

[clang] [clang] explicitly check if ParentMap contains key (PR #121736)

https://github.com/ssahasra created https://github.com/llvm/llvm-project/pull/121736 The implementation of ParentMap assumes that the key is absent if it is mapped to nullptr. This breaks when trying to store a tuple as the value type. Remove this assumption by explicit uses of `contains()` an