Fatal error when using submodules

I am using a submodule and want to run some CI tests.

When running the CI job it outputs

Checking out 7438d161 as master...
Updating/initializing submodules recursively...
Synchronizing submodule url for 'yapic/test_data'
fatal: Not a git repository: ../../.git/modules/yapic/test_data
fatal: Not a git repository: ../../.git/modules/yapic/test_data
fatal: Not a git repository: ../../.git/modules/yapic/test_data
fatal: Not a git repository: ../../.git/modules/yapic/test_data
Cannot chdir to , the toplevel of the working tree
ERROR: Job failed: exit code 1

My submodule is lying under ./yapic/test_data and the .git file reads

gitdir: ../../.git/modules/yapic/test_data

From my point of view this path should be fine because it expands to ./yapic/test_data…/…/.git/modules/yapic/test_data which exists, doesn’t it?

Any help would be very apprechiated!

Thanks!

Manuel