Make {{|=}} build correctly; add a test for this.

mwparserfromhell/parser/builder.py

@@ -83,7 +83,7 @@ class Builder(object):
                                     tokens.TemplateClose)):
                 self._tokens.append(token)
                 value = self._pop()
-                if not key:
+                if key is None:
                     key = self._wrap([Text(str(default))])
                 return Parameter(key, value, showkey)
             else:

tests/test_builder.py

@@ -72,6 +72,14 @@ class TestBuilder(TreeEqualityTestCase):
              wrap([Template(wraptext("foo"), params=[
                  Parameter(wraptext("bar"), wraptext("baz"))])])),
 
+            ([tokens.TemplateOpen(), tokens.TemplateParamSeparator(),
+              tokens.TemplateParamSeparator(), tokens.TemplateParamEquals(),
+              tokens.TemplateParamSeparator(), tokens.TemplateClose()],
+             wrap([Template(wrap([]), params=[
+                 Parameter(wraptext("1"), wrap([]), showkey=False),
+                 Parameter(wrap([]), wrap([]), showkey=True),
+                 Parameter(wraptext("2"), wrap([]), showkey=False)])])),
+
             ([tokens.TemplateOpen(), tokens.Text(text="foo"),
               tokens.TemplateParamSeparator(), tokens.Text(text="bar"),
               tokens.TemplateParamEquals(), tokens.Text(text="baz"),