better error handling while srcset creation is needed

[1letter]

in a template i define two tags:

<metal:row define-macro="teaser"
             tal:define="
               plone_view python:context.restrictedTraverse('@@plone');
               obj item/getObject;
               scale nocall:obj/@@images;
               tag python:scale.tag('image', width=800, height=350, mode='contain', loading='lazy');
               tag1 python: scale.srcset('image', width=1600, height=700, mode='contain', css_class='cover', loading='lazy', fetchpriority='high', alt=getattr(context, 'image_caption', None));
             "
  >

the srcset creation is broken if the imagefield is empty, the tag creation works without errors (it return None)

File "/opt/ukdd-p6.1/.venv/lib/python3.12/site-packages/plone/namedfile/scaling.py", line 803, in srcset
    attributes["src"] = scale.url
                        ^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'url'