relates to both #236 and #237. it's better support of Empty and needs…

… being documented.

bauble/search.py

@@ -70,6 +70,13 @@ def __repr__(self):
     def express(self):
         return set()
 
+    def __eq__(self, other):
+        if isinstance(other, EmptyToken):
+            return True
+        if isinstance(other, set):
+            return len(other) == 0
+        return NotImplemented
+
 
 class ValueABC(object):
     ## abstract base class.
@@ -1013,7 +1020,10 @@ def get_expression(self):
         and_or = ''
         if self.and_or_combo:
             and_or = self.and_or_combo.get_active_text()
-        result = ' '.join([and_or, self.prop_button.props.label,
+        field_name = self.prop_button.props.label
+        if value == EmptyToken():
+            field_name = field_name.rsplit('.', 1)[0]
+        result = ' '.join([and_or, field_name,
                            self.cond_combo.get_active_text(),
                            repr(value)]).strip()
         return result

bauble/test/test_search.py

@@ -959,3 +959,19 @@ def test_parse_typed_value_empty_set(self):
     def test_parse_typed_value_fallback(self):
         result = search.parse_typed_value('whatever else')
         self.assertEquals(result, 'whatever else')
+
+
+class EmptySetEqualityTest(unittest.TestCase):
+    def test_EmptyToken_equals(self):
+        et1 = search.EmptyToken()
+        et2 = search.EmptyToken()
+        self.assertEquals(et1, et2)
+        self.assertTrue(et1 == et2)
+        self.assertTrue(et1 == set())
+
+    def test_empty_token_otherwise(self):
+        et1 = search.EmptyToken()
+        self.assertFalse(et1 is None)
+        self.assertFalse(et1 == 0)
+        self.assertFalse(et1 == '')
+        self.assertFalse(et1 == set([1, 2, 3]))