fix default block size for dynamic launch grids

src/pystencilssfg/composer/gpu_composer.py

@@ -186,13 +186,8 @@ class SfgGpuComposer(SfgComposerMixIn):
 
                 block_size_init_args: tuple[ExprLike, ...]
                 if user_block_size is None:
-                    if launch_config.block_size is None:
-                        raise ValueError(
-                            "Neither a user-defined nor a default block size was defined."
-                        )
-
                     block_size_init_args = tuple(
-                        str(bs) for bs in launch_config.block_size
+                        str(bs) for bs in launch_config.default_block_size
                     )
                 else:
                     block_size_init_args = (user_block_size,)