How to disable a warning in Delphi about “return value … might be undefined”?

Result := '';

{$WARN NO_RETVAL OFF}
function func(...): string;
begin
  ...
end;
{$WARN NO_RETVAL ON}

program TestCompilerProblems;

procedure Proc;
var
  a01, a02, a03, a04, a05, a06, a07, a08, a09, a10,
  a11, a12, a13, a14, a15, a16, a17, a18, a19, a20,
  a21, a22, a23, a24, a25, a26, a27, a28, a29, a30,
  a31, a32, a33, a34, a35, a36, a37, a38, a39, a40: Integer;
begin
end;

begin
  Proc;
end.