fix assertion error #950

Job	Run time
static analysis (Elixir 1.14.x \| Erlang/OTP 25.x)	24s
mix test (Elixir 1.13.x \| Erlang/OTP 22.x)	5m 25s
mix test (Elixir 1.13.x \| Erlang/OTP 23.x)	6m 16s
mix test (Elixir 1.13.x \| Erlang/OTP 24.x)	4m 24s
mix test (Elixir 1.13.x \| Erlang/OTP 25.x)	3m 59s
mix test (Elixir 1.14.x \| Erlang/OTP 23.x)	6m 16s
mix test (Elixir 1.14.x \| Erlang/OTP 24.x)	4m 27s
mix test (Elixir 1.14.x \| Erlang/OTP 25.x)	3m 48s
mix test (Elixir 1.15.x \| Erlang/OTP 24.x)	4m 28s
mix test (Elixir 1.15.x \| Erlang/OTP 25.x)	3m 44s
mix test windows (Elixir 1.13.x \| Erlang/OTP 22.x)	9m 0s
mix test windows (Elixir 1.13.x \| Erlang/OTP 23.x)	9m 47s
mix test windows (Elixir 1.13.x \| Erlang/OTP 24.x)	7m 9s
mix test windows (Elixir 1.13.x \| Erlang/OTP 25.x)	7m 5s
mix test windows (Elixir 1.14.x \| Erlang/OTP 23.x)	8m 40s
mix test windows (Elixir 1.14.x \| Erlang/OTP 24.x)	6m 10s
mix test windows (Elixir 1.14.x \| Erlang/OTP 25.x)	6m 9s
mix test windows (Elixir 1.15.x \| Erlang/OTP 24.x)	7m 3s
mix test windows (Elixir 1.15.x \| Erlang/OTP 25.x)	5m 32s
	1h 49m 46s

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