Avoid TypeError parsing a property name containing '@'

cssutils/util.py

@@ -468,6 +468,13 @@ def _parse(
         """
         wellformed = True
 
+        if new is None:
+            # ``new`` is optional, but the default productions record the
+            # wellformed state into it (new['wellformed'] = False). Give them a
+            # throwaway dict when a caller that does not track it (e.g. parsing
+            # a bare property name) passes None, to avoid a TypeError.
+            new = {}
+
         if initialtoken:
             # add initialtoken to tokenizer
             def tokens():

tests/test_cssstyledeclaration.py

@@ -33,6 +33,19 @@ def test_init(self):
         assert 'top: 0' == s.cssText
         assert sheet == s.parentRule
 
+    def test_at_in_property_name(self):
+        "CSSStyleDeclaration with an '@' in a property name"
+        # A property name containing '@' reached the default productions with
+        # new=None and used to raise TypeError ('NoneType' object does not
+        # support item assignment). It should be reported as a normal CSS
+        # error instead: parsing a whole sheet drops the bad property and keeps
+        # the rest, and building a declaration directly raises SyntaxErr.
+        sheet = cssutils.parseString('a { col@or: red; width: 1px }')
+        assert '1px' == sheet.cssRules[0].style.getPropertyValue('width')
+
+        with pytest.raises(xml.dom.SyntaxErr):
+            cssutils.css.CSSStyleDeclaration(cssText='col@or: red')
+
     def test_items(self):
         "CSSStyleDeclaration[CSSName]"
         s = cssutils.css.CSSStyleDeclaration()