module T

`sig {params(arg: T.nilable(A), reason_blk: T.proc.returns(String)).returns(A)}`

to contain a non-nil value at this point.
Intended to be used to promise sorbet that a given nilable value happens

needs_foo(foo)
raise "reason_foo_should_not_be_nil" if foo.nil?
foo = maybe_gives_foo

Equivalent to:

needs_foo(T.must_because(maybe_gives_foo) {"reason_foo_should_not_be_nil"})

Intended to be used as:

is `nil` and return it otherwise.
A convenience method to `raise` with a provided error reason when the argument

def self.must_because(arg)
  return arg if arg
  return arg if arg == false
  begin
    raise TypeError.new("Unexpected `nil` because #{yield}")
  rescue TypeError => e # raise into rescue to ensure e.backtrace is populated
    T::Configuration.inline_type_error_handler(e, {kind: 'T.must_because', value: arg, type: nil})
  end
end