Bring guideline invariants up to spec

src/ufoLib2/objects/guideline.py

@@ -17,13 +17,13 @@ class Guideline(AttrDictMixin):
     data composition restrictions.
     """
 
-    x: Optional[float] = None
+    x: float = 0
     """The origin x coordinate of the guideline."""
 
-    y: Optional[float] = None
+    y: float = 0
     """The origin y coordinate of the guideline."""
 
-    angle: Optional[float] = None
+    angle: float = 0
     """The angle of the guideline."""
 
     name: Optional[str] = None
@@ -36,13 +36,5 @@ class Guideline(AttrDictMixin):
     """The globally unique identifier of the guideline."""
 
     def __attrs_post_init__(self) -> None:
-        x, y, angle = self.x, self.y, self.angle
-        if x is None and y is None:
-            raise ValueError("x or y must be present")
-        if x is None or y is None:
-            if angle is not None:
-                raise ValueError("if 'x' or 'y' are None, 'angle' must not be present")
-        if x is not None and y is not None and angle is None:
-            raise ValueError("if 'x' and 'y' are defined, 'angle' must be defined")
-        if angle is not None and not (0 <= angle <= 360):
+        if not (0 <= self.angle <= 360):
             raise ValueError("angle must be between 0 and 360")

tests/test_converters.py

@@ -110,7 +110,11 @@
                 ],
             },
         ),
-        (Guideline(x=0, name="foo"), {"x": 0, "name": "foo"}),
+        (Guideline(x=0, name="foo"), {"name": "foo"}),
+        (
+            Guideline(x=149, y=1523, identifier="aaa"),
+            {"x": 149, "y": 1523, "identifier": "aaa"},
+        ),
         (Guideline(y=1, name="bar"), {"y": 1, "name": "bar"}),
         (
             Guideline(