This question was asked and I first flagged it as a duplicate as it seemed to be one. After taking a little time to research, found out a bug report on the class the person was using. Added a comment so he could check if that was the case and indeed it was. Now, since this could affect other people coming to the site and helped the asker solve his problem, I answered providing the link. Was I right to do it? I feel it might not have been appropriate.
If you no longer think it's a duplicate, you should revoke your close vote, add a comment saying you don't think it's a dupe, and provide a substantive answer that could include a link but is still useful even if the link dies.
If you still think it's a dupe, add the substantive answer to the original.
If you now aren't sure whether it's a dupe or not and aren't willing to write a substantive answer but just wanted to provide the link to be helpful, leave the link in a comment on the question (and possibly also on the original question) and at least know you helped a little. Consider returning to give the substantive answer when you have a chance.
From How to Answer
Answer the question
Read the question carefully. What, specifically, is the question asking for? Make sure your answer provides that – or a viable alternative. The answer can be “don’t do that”, but it should also include “try this instead”. Any answer that gets the asker going in the right direction is helpful, but do try to mention any limitations, assumptions or simplifications in your answer. Brevity is acceptable, but fuller explanations are better.
Provide context for links
A link to a potential solution is always welcome, but please add context around the link so your fellow users will have some idea what it is and why it’s there . Always quote the most relevant part of an important link, in case the target site is unreachable or goes permanently offline.
I think the above 2 mostly apply in your case.
Remember, you are the judge. If you think your answer/link is useful, just make sure your follow the other guidelines.
For example, place the link and:
tell what's it regarding
how it helps answer the question in relation to its content
give some more useful information from the heart :)
Your duplicate flag should have been declined anyway by the reviewer. Note you can always flag it again specifying a custom message.