[instantiator] use designspace.findDefault() which in turns sets desi…

…gnspace.default

otherwise a DS object created from code (as opposed to one loaded from string or file) has a 'default' attribute set to None (until findDefault() is first called).

Lib/ufo2ft/instantiator.py

@@ -251,7 +251,7 @@ def from_designspace(
         do_glyphs=True,
     ):
         """Instantiates a new data class from a Designspace object."""
-        if designspace.default is None:
+        if designspace.findDefault() is None:
             raise InstantiatorError(_error_msg_no_default(designspace))
 
         if any(hasattr(axis, "values") for axis in designspace.axes):

tests/instantiator_test.py

@@ -71,7 +71,6 @@ def test_default_groups_only(ufo_module, data_dir, caplog):
     d.addSourceDescriptor(location={"Weight": 300}, font=ufo_module.Font())
     d.addSourceDescriptor(location={"Weight": 900}, font=ufo_module.Font())
     d.addInstanceDescriptor(styleName="2", location={"Weight": 400})
-    d.findDefault()
 
     d.sources[0].font.groups["public.kern1.GRK_alpha_alt_LC_1ST"] = [
         "alpha.alt",
@@ -102,7 +101,6 @@ def test_default_groups_only2(ufo_module, data_dir, caplog):
     d.addSourceDescriptor(location={"Weight": 300}, font=ufo_module.Font())
     d.addSourceDescriptor(location={"Weight": 900}, font=ufo_module.Font())
     d.addInstanceDescriptor(styleName="2", location={"Weight": 400})
-    d.findDefault()
 
     d.sources[0].font.groups["public.kern1.GRK_alpha_alt_LC_1ST"] = [
         "alpha.alt",