ezt: handle NoneFieldVar values (#78017)

tests/test_formdata.py

@@ -701,6 +701,7 @@ def variable_test_data(pub):
         fields.StringField(id='12', label='float1', varname='value', type='string'),
         fields.PasswordField(id='13', label='pwd', varname='pwd'),
         fields.EmailField(id='14', label='email', varname='email', type='email'),
+        fields.ItemField(id='15', label='item', items=['aa', 'bb', 'cc'], type='item', varname='itemfield'),
     ]
     formdef.workflow_roles = {'_receiver': role.id}
     formdef.geolocations = {'base': 'Base'}
@@ -2617,6 +2618,9 @@ def test_lazy_ezt_templates(pub, variable_test_data):
     tmpl = Template('[form_user_name_identifier_0]')
     assert tmpl.render(context) == pub.user_class.select()[0].name_identifiers[0]
 
+    tmpl = Template('[form_var_itemfield]')
+    assert tmpl.render(context) == ''
+
 
 def test_lazy_formdata_fields(pub):
     formdef = FormDef()

wcs/qommon/ezt.py

@@ -679,6 +679,11 @@ def _get_value(value_ref, ctx):
         return str(ob)
     if ob is None:
         return ''
+    # specific wcs None lazy value
+    from ..variables import NoneFieldVar
+
+    if isinstance(ob, NoneFieldVar):
+        return ''
 
     # string or a sequence
     return ob