Set title / url for associated resources to empty string if not defined

[josegar74]

Previously these values were set as null, displaying that text in the user interface.

For example, for a service referencing a remote dataset using srv:operatesOn, the dataset info was displayed like:

With the change, the following code works fine, displaying the url value:

https://github.com/geonetwork/core-geonetwork/blob/6e2f05ecc93f6c82a6f3ebb095ba33f45a304ef0/web-ui/src/main/resources/catalog/components/metadataactions/partials/metadataCard.html#L24

[ianwallen]

Related to #5081 Looks like this fix should fix the issue so that there is a link to be clicked however it still seems odd to allow null/empty titles. Also note that the title is most likely used in a lot of other locations that may cause issues when empty/null

However this is an improvement :+1:

Will this be backported to 3.12.x?

[josegar74]

@ianwallen this PR is not really related to #5081. The change affect the related resources, when the related resource title is not available, usually if could not be extracted during the metadata indexing.