replaceAll functionality in UDF does not work for forwardslash

[natarajank11]

trino 407:

`

public static Slice rmesc(@SqlType(StandardTypes.VARCHAR) Slice string)
{
String text = string.toStringUtf8();
return Slices.utf8Slice(text.replaceAll("(\\,)", ",").replaceAll("(\\\\)", "\"));
}

`

The above UDF does not produce the expected value.
trino> select rmesc('\\,'); => \,
trino> select rmesc('\\\\'); => failed: character to be escaped is missing

I tried to reproduce with replace function instead of replaceAll, it works fine as per expectation.
return Slices.utf8Slice(text.replace("\\\\,", ",").replace("\\\\\\\\", "\\"));
This produces correct output,
trino> select rmesc('\\,'); => ,
trino> select rmesc('\\\\'); => \