"Build config did not create any jobs" when only one version of python is specified

When I specify multiple python versions like below, travis initiates testing.

python:
  - "3.7"
  - "3.8"

(from https://github.com/biocommons/uta-align/blob/05a6d088d66ce911e934b1c085c173fdefd65a7b/.travis.yml)

If I remove either version line so that only one version is specified, travis (nearly) silently ignores the push. The requests page shows “Build config did not create any jobs.”

If I specify 3.7 twice, it works but initiates only one 3.7 run.

Both of these behaviors surprise me.

In https://github.com/biocommons/uta-align/blob/43cd96db6956f45fa1b7f6a3affe9b1ad3e436bd/.travis.yml the explicit job definition is invalid due to password specified incorrectly.

The job from matrix is not created because https://docs.travis-ci.com/user/build-matrix/#explicitly-included-jobs-with-only-one-element-in-the-build-matrix.


You can now check your .travis.yml at https://config.travis-ci.com/explore.

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