JENKINS-28188 StringIndexOutOfBoundsException when no root cause

[dcoraboeuf]

When a build has no root cause (possible when firing the job programmatically), the code at org.jenkinsci.plugins.envinject.service.BuildCauseRetriever#buildCauseEnvironmentVariables produces a StringIndexOutOfBoundsException because the substring method is applied to an empty string.

The fix I propose is very basic and could be simplified using Guava - but I didn't date to use it in this plugin.

[oleg-nenashev]

I suppose StringUtils.join() could resolve the issue in a more elegant way. BTW, we would still need a cycle (and null/empty string checks), so LGTM

[dcoraboeuf]

Yes, StringUtils, of course :( I'll adjust accordingly.

[dcoraboeuf]

Done.

[jenkinsadmin]

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[dcoraboeuf]

Tests are failing in Cloudbees, not locally. I'll have a look later on.

[dcoraboeuf]

The failure has nothing to do with this PR - it was already there before.

[oleg-nenashev]

LGTM. Thanks for the fix

[lanwen]

This is same as #45 (there is test for it)

[oleg-nenashev]

Closing in a favor of #45
@dcoraboeuf thanks for you efforts. The original title in #45 was too narrow specific, so unfortunately I have not noticed a duplication on early stages.