Validate default values

[todvora]

So far we have ignored validation of default values. These are given by us, as a field value of the configuration property. This would be a valid configuration that causes no errors during init:

@Parameter(value = "test.positive.long", validator = PositiveLongValidator.class)
private long myPositiveLong = -1;

But it's obviously wrong and will cause, sooner or later, problems elsewhere. That's why I believe is correct to validate default values as well.

In the best case, we would validate these during compile time, not during run time. But some of the properties are paths and config related to the running system, so we are unable to determine if the value is correct or not during compilation. Runtime check is the next best thing to avoid problems later in the execution.

Notes for Reviewers

• The commit history must be preserved - please use the rebase-merge or standard merge option instead of squash-merge
• Sync up with the author before merging

[luk-kaminski]

LGTM, thanks!

[thll]

I like the new behaviour, but it can break existing applications so we have to make sure that we state that clearly as a breaking change in the release.