Url field vanishes after running "Check integrity"

[Siedlerchr]

Originally reported by Sait_Umar in the forum:

http://discourse.jabref.org/t/check-integrity-removing-my-url-fields/123/4

JabRef 3.5 and Jabref 3.6dev
windows 7 6.1 amd64
Java 1.8.0_102

Tested both biblatex and bibtex entries:

Steps to reproduce:

1. Create a new bib database (In file.bib some entries contain url fields)
2. Enter entry with url content http:://www.google.de
3. Run "check integrity..."
4. Make a small correction at some place, e.g. change the title
5. save database
6. See if url fields are still there.

=> After saving the url field is completely vanished

No errors, no info in log file

[oscargus]

Caused by:

            // the url field should not be checked for hashes, as they are legal in this field
            fields.remove(FieldName.URL);