Handle empty list in content view parameter

Summary: Fix the EL expression returned when using the NXQL IN operator and the list returned by the EL is empty

schema:field IN ?
=> The EL is using a NULL field or the ('') expression

More details
I have a multivalued string field, activity:issues
It contains references (uid) to documents (IssueDocument) and is filled using the "multiple document suggestion" widget.
Then in another place (a tab) I need to display the list of issues in a content view. The NXQL filter for this content-view is just:

ecm:uuid IN ?

The parameter is:

#{currentDocument.activity.issues}

This works only if the filed is not empty (not null probably, for example when a new document is created). If it is empty, an error is displayed:

Failed to execute query: org.nuxeo.ecm.core.query.QueryParseException: Syntax error: Invalid token <)> at offset 43 in query: SELECT * FROM Document WHERE (ecm:uuid IN ()) ORDER BY dc:title

=> We can see the expression returned just () instead of ('') with the quotes.
So I added a condition to the parameter:

#{empty currentDocument.activity.issues ? ('') ? currentDocument.activity.issues}

The problem is that it still doesn't work if the list is empty. Like if at runtime, the parenthesis were removed:

Syntax error: Invalid token <> at offset 43 in query: SELECT * FROM Document WHERE (ecm:uuid IN '') 

I tried by changing the filter to add the parenthesis:

ecm:uuid IN (?)

But then the error is displayed when there is at least one value, because the expression adds the parenthesis too so we have "((":

Syntax error: Invalid token <(> at offset 43 in query: SELECT * FROM Document WHERE (ecm:uuid IN (('9c1178b3-b6ff-4db9-99d8-688f61195a45'))

The workaround found is about having an activity:issues_empty multivalued string field. For "about to create document" event, this field is filled with an empty string. Then, the ternary operator in the EL returns this field:

#{empty currentDocument.activity.issues ? currentDocument.activity.issues_empty ? currentDocument.activity.issues}