{:ok, nil} -> {:error, :not_found} in handle_get_block_by_tag

Fixes #490

Compatibility with openethereum/parity-ethereum#8281, which fixed
openethereum/parity-ethereum#8028 and made pending return be compliant
with Ethereum docs.

apps/ethereum_jsonrpc/lib/ethereum_jsonrpc.ex

@@ -194,7 +194,7 @@ defmodule EthereumJSONRPC do
 
   """
   @spec fetch_block_number_by_tag(tag(), json_rpc_named_arguments) ::
-          {:ok, non_neg_integer()} | {:error, reason :: :invalid_tag | term()}
+          {:ok, non_neg_integer()} | {:error, reason :: :invalid_tag | :not_found | term()}
   def fetch_block_number_by_tag(tag, json_rpc_named_arguments) when tag in ~w(earliest latest pending) do
     tag
     |> get_block_by_tag_request()
@@ -438,6 +438,10 @@ defmodule EthereumJSONRPC do
     {:ok, quantity_to_integer(quantity)}
   end
 
+  # https://github.com/paritytech/parity-ethereum/pull/8281 fixed
+  #   https://github.com/paritytech/parity-ethereum/issues/8028
+  defp handle_get_block_by_tag({:ok, nil}), do: {:error, :not_found}
+
   defp handle_get_block_by_tag({:error, %{"code" => -32602}}), do: {:error, :invalid_tag}
   defp handle_get_block_by_tag({:error, _} = error), do: error
 end

apps/ethereum_jsonrpc/test/ethereum_jsonrpc/mox_test.exs

@@ -0,0 +1,33 @@
+defmodule EthereumJSONRPC.MoxTest do
+  @moduledoc """
+  Tests that only work with `EthereumJSONRPC.Mox` because they need precise data back from the network that can't be
+  gotten reliably.
+  """
+
+  use ExUnit.Case, async: true
+
+  import EthereumJSONRPC.Case, only: [variant: 0]
+  import Mox
+
+  setup do
+    %{
+      json_rpc_named_arguments: [
+        transport: EthereumJSONRPC.Mox,
+        transport_options: [],
+        variant: variant()
+      ]
+    }
+  end
+
+  setup :verify_on_exit!
+
+  describe "fetch_block_number_by_tag/2" do
+    test "with pending with null result", %{json_rpc_named_arguments: json_rpc_named_arguments} do
+      expect(EthereumJSONRPC.Mox, :json_rpc, fn _json, _options ->
+        {:ok, nil}
+      end)
+
+      assert {:error, :not_found} = EthereumJSONRPC.fetch_block_number_by_tag("pending", json_rpc_named_arguments)
+    end
+  end
+end

apps/ethereum_jsonrpc/test/ethereum_jsonrpc_test.exs

@@ -200,15 +200,21 @@ defmodule EthereumJSONRPCTest do
     test "with pending", %{json_rpc_named_arguments: json_rpc_named_arguments} do
       if json_rpc_named_arguments[:transport] == EthereumJSONRPC.Mox do
         expect(EthereumJSONRPC.Mox, :json_rpc, fn _json, _options ->
-          {:ok, %{"number" => "0x2"}}
+          {:ok, nil}
         end)
       end
 
       log_bad_gateway(
         fn -> EthereumJSONRPC.fetch_block_number_by_tag("pending", json_rpc_named_arguments) end,
-        fn result ->
-          assert {:ok, number} = result
-          assert number > 0
+        fn
+          # Parity after https://github.com/paritytech/parity-ethereum/pull/8281 and anything spec-compliant
+          {:error, reason} ->
+            assert reason == :not_found
+
+          # Parity before https://github.com/paritytech/parity-ethereum/pull/8281
+          {:ok, number} ->
+            assert is_integer(number)
+            assert number > 0
         end
       )
     end