white space in the mechanism reference id

[piotr-gawron]

When you return this webpage from api:
https://www.ebi.ac.uk/chembl/api/data/mechanism?molecule_chembl_id=CHEMBL2103846

There is whitespace in the PUBMED identifier (and in the end of url):

<mechanism>
  <ref_id>18216291 </ref_id>
  <ref_type>PubMed</ref_type>
  <ref_url>http://europepmc.org/abstract/MED/18216291 </ref_url>
</mechanism>

I know that in the schema the definition is string, but I think this space is making the identifier wrong.