fields: keep display_locations empty value on import (#48969)

tests/test_formdef_import.py

@@ -86,6 +86,36 @@ def test_empty_description_tag():
     assert not formdef2.description
 
 
+def test_empty_display_locations_tag():
+    formdef = FormDef()
+    formdef.name = 'Foo'
+    formdef.fields = [
+        fields.TitleField(type='title', label='title', display_locations=[]),
+        fields.SubtitleField(type='subtitle', label='subtitle', display_locations=[]),
+        fields.TextField(type='text', label='string', display_locations=[]),
+    ]
+
+    formdef_xml = formdef.export_to_xml()
+    f1 = formdef_xml.findall('fields/field')[0]
+    f2 = formdef_xml.findall('fields/field')[1]
+    f3 = formdef_xml.findall('fields/field')[2]
+    assert '<display_locations />' in str(ET.tostring(f1))
+    assert '<display_locations />' in str(ET.tostring(f2))
+    assert '<display_locations />' in str(ET.tostring(f3))
+
+    formdef2 = assert_xml_import_export_works(formdef)
+    assert formdef2.fields[0].display_locations == []
+    assert formdef2.fields[1].display_locations == []
+    assert formdef2.fields[2].display_locations == []
+    formdef2_xml = formdef2.export_to_xml()
+    f1 = formdef2_xml.findall('fields/field')[0]
+    f2 = formdef2_xml.findall('fields/field')[1]
+    f3 = formdef2_xml.findall('fields/field')[2]
+    assert '<display_locations />' in str(ET.tostring(f1))
+    assert '<display_locations />' in str(ET.tostring(f2))
+    assert '<display_locations />' in str(ET.tostring(f3))
+
+
 def test_boolean_attributes():
     formdef = FormDef()
     formdef.name = 'Foo'

wcs/fields.py

@@ -349,7 +349,10 @@ class Field(object):
                 setattr(self, attribute, v)
             else:
                 if el.text is None:
-                    setattr(self, attribute, None)
+                    if isinstance(getattr(self, attribute), list):
+                        setattr(self, attribute, [])
+                    else:
+                        setattr(self, attribute, None)
                 elif el.text in ('False', 'True'):  # bools
                     setattr(self, attribute, el.text == 'True')
                 elif type(getattr(self, attribute)) is int: