Don't fail if 'id' is missing from an object. (#464)

The goal here is to give us the freedom to drop 'id' from FreeObject.

edgedb/datatypes/object.c

@@ -51,13 +51,6 @@ EdgeObject_New(PyObject *desc)
         return NULL;
     }
 
-    if (EdgeRecordDesc_IDPos(desc) < 0) {
-        PyErr_SetString(
-            PyExc_ValueError,
-            "Cannot create Object without 'id' field");
-        return NULL;
-    }
-
     Py_ssize_t size = EdgeRecordDesc_GetSize(desc);
 
     if (size > EDGE_MAX_TUPLE_SIZE) {
@@ -137,7 +130,10 @@ EdgeObject_GetID(PyObject *ob)
     assert(EdgeObject_Check(ob));
     EdgeObject *o = (EdgeObject *)ob;
     Py_ssize_t i = EdgeRecordDesc_IDPos(o->desc);
-    if (i < 0 || i >= Py_SIZE(o)) {
+    if (i < 0) {
+        Py_RETURN_NONE;
+    }
+    if (i >= Py_SIZE(o)) {
         PyErr_BadInternalCall();
         return NULL;
     }

tests/datatypes/test_datatypes.py

@@ -561,8 +561,8 @@ def test_object_5(self):
             lb='link-property',
             c='property'
         )
-        with self.assertRaisesRegex(ValueError, "without 'id' field"):
-            f(1, 2, 3)
+        x = f(1, 2, 3)
+        self.assertFalse(hasattr(x, 'id'))
 
     def test_object_6(self):
         User = private.create_object_factory(