Trying to fix "Coverage build failure"

I am trying to understand this failure: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=51785

The failure log at
https://oss-fuzz-build-logs.storage.googleapis.com/log-3d5872dd-c2f8-4192-b6a0-989da7116fb9.txt
includes the following, at the end:

```
Starting Step #5
Step #5: Already have image (with digest): gcr.io/oss-fuzz-base/base-runner
Step #5: warning [/corpus/UtilCheckerFuzzer.zip]: zipfile is empty
Step #5: Failed to unpack the corpus for UtilCheckerFuzzer. This usually means that corpus backup for a particular fuzz target does not exist. If a fuzz target was added in the last 24 hours, please wait one more day. Otherwise, something is wrong with the fuzz target or the infrastructure, and corpus pruning task does not finish successfully.
Step #5: ********************************************************************************
Step #5: Code coverage report generation failed.
Step #5: To reproduce, run:
Step #5: python infra/helper.py build_image checker-framework
Step #5: python infra/helper.py build_fuzzers --sanitizer coverage checker-framework
Step #5: python infra/helper.py coverage checker-framework
Step #5: ********************************************************************************
Finished Step #5
ERROR
ERROR: build step 5 "gcr.io/oss-fuzz-base/base-runner" failed: step exited with non-zero status: 1
```

This has been ongoing longer than 24 hours.
Can you advise on how to fix this?

The webpage https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=51785 says:

> To reproduce locally, please see: https://google.github.io/oss-fuzz/advanced-topics/reproducing#reproducing-build-failures

Then, https://google.github.io/oss-fuzz/advanced-topics/reproducing#reproducing-build-failures says:

> Every issue has a reproducer file (also know as a “testcase” file) attached. Download it.

I don't know where to find that file.

More generally, since I didn't set this up (someone from code-intelligence kindly did!), I'm at a bit of a loss as to how to proceed.

Thank you for your help.

Start with the linked OSS-Fuzz failure and the end of the provided build log, then run the three listed commands in infra/helper.py for checker-framework. Inspect the coverage step and the UtilCheckerFuzzer corpus warning. Done means identifying why coverage report generation fails and documenting a reproducible fix or next diagnostic step.

Written by the indexing model from the issue text.