Handle nil quantities in block decoding routine

Uncle block fetched using eth_getUncleByBlockHashAndIndex API may have
null in their size field. We shouldn't crash in this case.

apps/ethereum_jsonrpc/lib/ethereum_jsonrpc/block.ex

@@ -435,10 +435,15 @@ defmodule EthereumJSONRPC.Block do
   end
 
   defp entry_to_elixir({key, quantity})
-       when key in ~w(difficulty gasLimit gasUsed minimumGasPrice number size totalDifficulty) do
+       when key in ~w(difficulty gasLimit gasUsed minimumGasPrice number size totalDifficulty) and not is_nil(quantity) do
     {key, quantity_to_integer(quantity)}
   end
 
+  # Size may be `nil` for uncle blocks
+  defp entry_to_elixir({key, nil}) when key in ~w(size) do
+    {key, nil}
+  end
+
   # double check that no new keys are being missed by requiring explicit match for passthrough
   # `t:EthereumJSONRPC.address/0` and `t:EthereumJSONRPC.hash/0` pass through as `Explorer.Chain` can verify correct
   # hash format