Simplify code. Remove redundant casts and checks.

From sources/javadoc:
hudson.model.AbstractProject#getTrigger(Class<T> clazz)
* Gets the specific trigger, or null if the propert is not configured for this job.
A method doesn't need to be used in more than one place in order to be created. It's really a style issue, as performance isn't affected. We generally try to break everything up into logical sections when we can. I'd say if we are going to include this here, then it should be:
```
values.add(new StringParameterValue("ghprbActualCommitAuthor", cause.getCommitAuthor() != null ? getString(cause.getCommitAuthor().getName(), "") : ""));
values.add(new StringParameterValue("ghprbActualCommitAuthorEmail", cause.getCommitAuthor() != null ? getString(cause.getCommitAuthor().getEmail(), "") : ""));
```

I know it's longer, but it's more concise overall, and it reveals less of a reason for a separate method. I would actually pull the triggerAuthor and triggerAuthorEmail assignments into a different method, expand the try (which can surround both as they are the same error related to the same object), and print a log message when an error is encountered, as there is nothing printed for this Exception. Separating it into a separate method just makes it a more readable entity.