fields: fix display of optional item fields that have no items (#8769)

tests/test_fields.py

@@ -173,3 +173,15 @@ def test_item_render():
     field.add_to_form(form)
     assert str(form.render()).count('<option value="">Bla bla bla</option>') == 1 # ---
     assert str(form.render()).count('<option') == 4
+
+    # without any item
+    field = fields.ItemField(id='1', label='Foobar', items=[])
+    form = Form()
+    field.add_to_form(form)
+    assert str(form.render()).count('<option') == 1
+
+    # without any item and not being required
+    field = fields.ItemField(id='1', label='Foobar', items=[], required=False)
+    form = Form()
+    field.add_to_form(form)
+    assert str(form.render()).count('<option') == 1

wcs/fields.py

@@ -861,7 +861,7 @@ class ItemField(WidgetField):
             options = self.items[:]
         else:
             options = data_sources.get_items(self.data_source)
-        if not self.required:
+        if options and not self.required:
             if type(options[0]) is str:
                 options[:0] = [None]
             elif len(options[0]) == 2: