I have specified the package to publish to my NuGet feed with no wildcards, i.e.

agsimsetup.$BUILD_ID.nupkg

This works fine:

Starting agdev publication
[agsimsetup-dev] $ nuget push agsimsetup.2.2.1.0-build-69.nupkg ******** -Source https://api.bintray.com/nuget/aboutgolf/agdev -NonInteractive
Pushing agsimsetup.2.2.1.0-build-69.nupkg to 'https://api.bintray.com/nuget/aboutgolf/agdev'...
PUT https://api.bintray.com/nuget/aboutgolf/agdev/
Created https://api.bintray.com/nuget/aboutgolf/agdev/ 2021ms
Your package was pushed.
Ended agdev publication
Finished: SUCCESS

If, however, I specify a non-existing package no error is generated. For example, if the change the package to publish to:

agsimbadsetup.$BUILD_ID.nupkg

Then the publish still succeeds (though of course nothing is published):

Starting agdev publication
Ended agdev publication
Finished: SUCCESS

In this case I expect it to fail.