[erlang-questions] *WARNING* Missing application sasl. Can not upgrade with this release

[by]

Hello List,

Recently, I am trying to get familiar with "Creating and Upgrading a Target System”.
I follow the instructions which documented here: http://erlang.org/doc/system_principles/create_target.html <http://erlang.org/doc/system_principles/create_target.html>
And I am done with 3.1, but with a *WARNING* message saying: "*WARNING* Missing application sasl. Can not upgrade with this release”.
How can I suppress this message?

By the way, I come from rebar3, and just want to understand how the underlying release handing works in Erlang itself.

Best Regards,
Yao Bao
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