Don't format if 'withdrawals' coming back from get_block is null (#2941)

* Don't format if 'withdrawals' coming back from get_block is null

* Add newsfragment

Author: kclowes

newsfragments/2941.bugfix.rst

@@ -0,0 +1 @@
+Add check for null withdrawal field on get_block response

web3/_utils/method_formatters.py

@@ -297,7 +297,9 @@ def apply_list_to_array_formatter(formatter: Any) -> Callable[..., Any]:
         )
     ),
     "transactionsRoot": apply_formatter_if(is_not_null, to_hexbytes(32)),
-    "withdrawals": apply_formatter_to_array(withdrawal_result_formatter),
+    "withdrawals": apply_formatter_if(
+        is_not_null, apply_list_to_array_formatter(withdrawal_result_formatter)
+    ),
     "withdrawalsRoot": apply_formatter_if(is_not_null, to_hexbytes(32)),
 }