Resolve 'TypeError' in _setup_split_targets_build()

[9640-Akhil]

This change addresses a TypeError in _setup_split_targets_build(). The error arises when _get_targets_list() returns None, because there is an attempt to check for fuzz_target in a NoneType object. To fix this, a separate check has been introduced to verify that targets_list is not None before it is iterated over.

[aditya-wazir]

Added a check to ensure 'targets_list' is not None before attempting to iterate over it.

This needs to be reworded. Add error reporting link. there is one format we were following for health related issue. refer that

[9640-Akhil]

Mark:

Hello Akhil Kumar, thank you for taking the time to address this issue. A few thoughts:

1. This change indicates that the targets_list does not exist, which seems problematic. Do you have any insight as to why the list isn't being found?
2. Why would this change resolve a TypeError?
3. I noticed this is your first PR on the repo. We're happy to have your contributions. However, we always try to add test coverage when possible. Can you please add a testcase for this change in the below file?
   clusterfuzz/src/clusterfuzz/_internal/tests/core/build_management /build_manager_test.py

[9640-Akhil]

Hello @\marktefftech, thank you for the feedback. I've addressed your points below.

1. The _get_targets_list function returns None, when the targets.list file in the build's storage bucket is either missing or empty. As of today, we are seeing 3 jobs (libfuzzer_asan_android_host_nugget_os_emulator, libfuzzer_asan_android_host_sliderGSA, libfuzzer_asan_android_host_udfps) that are giving this error. When we checked theFUZZ_TARGET_BUILD_BUCKET_PATH for said jobs, the folder either ⁠doesn't exist or ⁠is empty.
2. The TypeError occurs because the original code attempts to check for the presence of fuzz_target within targets_list even when targets_list is None . The change adds a preliminary check/condition for this case, the first part of the condition. If it is indeed found to be None, then there is no iteration over targets_list successfully avoiding the TypeError and raising a BuildNotFoundError inside the check instead.
3. Thank you. I have added the testcase.