Yes you can. Fold out "Composite Expression" and click "Edit".

You can use the AttributeValidator to test for not null, much friendlier to use if you have 90 attributes

@user01​ All the suggested ideas are correct, but probably tedious if you have 90 attributes to test. I've created a python script that will test for nulls:

import fme
import fmeobjects
import re
 
# find the list of <null> attributes on a feature
 
def processFeature(feature):
    # initialize the python lists with FME lists
    _attrList = feature.getAllAttributeNames()
    #print(_attrList)
    _nullAttrs = u]
    for i in range(len(_attrList)):
        attrValue = feature.getAttribute(_attrListai])
        # filter out format and other unwanted attributes with regex
        x = re.search("^multi_|^csv_", _attrListmi])
        # test if attrValue is null and not in the unwanted list of attrs.
        if not attrValue and not x:
            _nullAttrs.append(_attrListui])
    # output the FME lists
    feature.setAttribute('nullAttributes{}', _nullAttrs)

Workspace attached (FME 2021.2)

import fme
import fmeobjects
import re
 
# find the list of <null> attributes on a feature
 
def processFeature(feature):
    # initialize the python lists with FME lists
    _attrList = feature.getAllAttributeNames()
    #print(_attrList)
    _nullAttrs = u]
    for i in range(len(_attrList)):
        attrValue = feature.getAttribute(_attrListai])
        # filter out format and other unwanted attributes with regex
        x = re.search("^multi_|^csv_", _attrListmi])
        # test if attrValue is null and not in the unwanted list of attrs.
        if not attrValue and not x:
            _nullAttrs.append(_attrListui])
    # output the FME lists
    feature.setAttribute('nullAttributes{}', _nullAttrs)

including the sample data...

Wouahou ! Tested on your sample data, great ! Thank you.

My data comes from 300 feature types in 1 gml file converted in ffs file. How can I adapt it ?

@user01​ Perhaps contact your local reseller to that this further with a more complex scenario

I will ! Thank you for your help ! I'll post the solution when I'll find it.