Fix BaseModel construction for required fields

Author: stainless-bot

lithic/_models.py

@@ -27,7 +27,7 @@ def construct(cls: Type[ModelT], _fields_set: set[str] | None = None, **values:
                 key = name
 
             if key in values:
-                if values[key] is None and not field.required:
+                if values[key] is None:
                     fields_values[name] = field.get_default()
                 else:
                     if not is_literal_type(field.type_) and (