Bugfix/5045 : Modified the existing logic to comply crossref resolution with biblatex specification

[CyraxSector]

Fixes #5045

---

• Change in CHANGELOG.md described
• Tests created for changes
• Manually tested changed features in running JabRef
• Screenshots added in PR description (for bigger UI changes)
• Ensured that the git commit message is a good one
• Check documentation status (Issue created for outdated help page at help.jabref.org?)

[Siedlerchr]

Thanks for your contribution. Could you please add a test for the changed code?

[tobiasdiez]

Thanks for your contribution. With your changes, the value of the field in the crossreferenced entry is always taken, even if it specified in the entry itself. This is not the problem descried in #5045 and not according to the biblatex specification.

The real problem is that biblatex specifies a more complex crossref resolution. I think a proper fix should go along the following lines:

if (!result.isPresent() && (database != null)) {
            Optional<BibEntry> referred = database.getReferencedEntry(this);
            if (!referred.isEmpty()) {
                  result = referred.get()..getFieldOrAlias(field);
                  if (result.isEmpty()) {
                       if (type == InProceedings && field = FieldNames.booktitle) {
                               result = referred.get().getFiledOrAlias(FieldName.title);
                       }
                      // Add other special cases that might be mentioned in the biblatex documentation
                   }
             }
        }

[CyraxSector]

@tobiasdiez @Siedlerchr sure I'll make those amendments and the UTs

[CyraxSector]

@tobiasdiez Could you please review the latest commit. Thanks :)

[Siedlerchr]

Looks good to me now.
Please merge the latest master changes in. There have been renaming of the Fields classes, so you need to fix this. Then we can merge

[CyraxSector]

Looks good to me now.
Please merge the latest master changes in. There have been renaming of the Fields classes, so you need to fix this. Then we can merge

@Siedlerchr I pulled the changes from master. This PR can be merged to the master now. Thanks

[Siedlerchr]

Please check your imports, it seems like you have imported the type from the wrong package.
Must be import org.jabref.model.entry.StandardEntryType;
And CrossRef here looks also odd.

[Siedlerchr]

Please review the imports.

[CyraxSector]

Please review the imports.

Fixed and organized imports. Please review and merge

[Siedlerchr]

Please review the imports.

Fixed and organized imports. Please review and merge

Please have a look at travis checkstyle output. Star imports are not allowed.
If you use Intellij you can directly import the code style from the config folder
For eclipse you can run ./gradlew eclipse to automatically import the correct code style

If you then run organize imports in the IDE it will be correct

[CyraxSector]

Please review the imports.

Fixed and organized imports. Please review and merge

Please have a look at travis checkstyle output. Star imports are not allowed.
If you use Intellij you can directly import the code style from the config folder
For eclipse you can run ./gradlew eclipse to automatically import the correct code style

If you then run organize imports in the IDE it will be correct

Fixed imports issue. Please review