A log for downloading a non-existent JAR, when there’s an actual download taking place will look like this:

/private/var/folders/0m/h2n902qn38b8555xq8z0w_h40000gn/T/process-executionaHl9Ym/.cache/jdk/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.6/scala-library-2.13.6.jar

stderr:
+ coursier_exe=__coursier/./cs-x86_64-apple-darwin
+ shift
+ json_output_file=coursier_report.json
+ shift
++ pwd
+ working_dir=/private/var/folders/0m/h2n902qn38b8555xq8z0w_h40000gn/T/process-executionaHl9Ym
+ __coursier/./cs-x86_64-apple-darwin fetch -r=<https://repo.osgeo.org/repository/geotools-releases> -r=<https://maven-central.storage-download.googleapis.com/maven2> --json-output-file=coursier_report.json org.scala-lang:scala-library:2.13.6 javax.media:jai_core:1.1.3
Downloading <https://repo1.maven.org/maven2/javax/media/jai_core/1.1.3/jai_core-1.1.3.pom>
Downloading <https://repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.6/scala-library-2.13.6.pom>
Downloaded <https://repo1.maven.org/maven2/javax/media/jai_core/1.1.3/jai_core-1.1.3.pom>
Downloaded <https://repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.6/scala-library-2.13.6.pom>
Downloading <https://repo1.maven.org/maven2/javax/media/jai_core/1.1.3/jai_core-1.1.3.jar>
Downloading <https://repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.6/scala-library-2.13.6.jar>
Downloaded <https://repo1.maven.org/maven2/javax/media/jai_core/1.1.3/jai_core-1.1.3.jar>
Downloading <https://repo1.maven.org/maven2/javax/media/jai_core/1.1.3/jai_core-1.1.3.jar.sha1>
Downloaded <https://repo1.maven.org/maven2/javax/media/jai_core/1.1.3/jai_core-1.1.3.jar.sha1>
Downloaded <https://repo1.maven.org/maven2/org/scala-lang/scala-library/2.13.6/scala-library-2.13.6.jar>
+ /bin/mkdir -p classpath
+ /Users/chrisjrn/.pyenv/versions/3.8.12/bin/python __coursier/coursier_post_processing_script.py coursier_report.json
Traceback (most recent call last):
  File "__coursier/coursier_post_processing_script.py", line 13, in <module>
    source = PurePath(dep['file'])
  File "/Users/chrisjrn/.pyenv/versions/3.8.12/lib/python3.8/pathlib.py", line 651, in __new__
    return cls._from_parts(args)
  File "/Users/chrisjrn/.pyenv/versions/3.8.12/lib/python3.8/pathlib.py", line 683, in _from_parts
    drv, root, parts = self._parse_args(args)
  File "/Users/chrisjrn/.pyenv/versions/3.8.12/lib/python3.8/pathlib.py", line 667, in _parse_args
    a = os.fspath(a)
TypeError: expected str, bytes or os.PathLike object, not NoneType

That’s is from yesterday — note all the `Downloading`/`Downloaded` lines. Those don’t appear in stderr if Coursier is using its cache