`Macro.underscore/1` - no match of right hand side value: "nil"

[up2jj]

Environment

• Elixir & Erlang/OTP versions (elixir --version):

  
  Erlang/OTP 26 [erts-14.2.3] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit]

Elixir 1.16.2 (compiled with Erlang/OTP 26)

- Operating system: Mac
- Pigeon version: 1.6.1

### Current behavior

We have started noticing the following error recently:

MatchError: no match of right hand side value: "nil" File "lib/macro.ex", line 2202, in Macro.underscore/1 File "lib/pigeon/fcm/config.ex", line 184, in Pigeon.Configurable.Pigeon.FCM.Config.parse_error/1 File "lib/pigeon/fcm/config.ex", line 142, in Pigeon.Configurable.Pigeon.FCM.Config.do_handle_end_stream/4 File "lib/pigeon/connection.ex", line 113, in Pigeon.Connection.process_end_stream/2 File "lib/gen_stage.ex", line 2206, in GenStage.noreply_callback/3 File "gen_server.erl", line 1095, in :gen_server.try_handle_info/3 File "gen_server.erl", line 1183, in :gen_server.handle_msg/6 File "proc_lib.erl", line 241, in :proc_lib.init_p_do_apply/3

I am not sure, if it is related the deprecation  https://firebase.google.com/docs/cloud-messaging/migrate-v1?hl=en&authuser=0