Fix bug related with pagination

There was a bug which avoided to render the errorCode with "details=on". Render methods have been modified and also some unit tests that were broken with the modifications.
ok.
It looks good, except that you need to put back the 'else'.
We must either render the contextElementResponseVector OR the errorCode (5.4.1.2 in OMS spec).
Your new implementation looks at the size of the response vector, which I guess is OK.

Perhaps we should protect ourselves against empty response vector AND unfilled errorCode?
I mean, one of the two must be rendered and if both of them are 'empty' then we should fill the errorCode right here before rendering?
Hard to explain this ...
If what I mean is not clear, then we need to talk.