A DESCRIPTION OF THE PROBLEM :
In Java 17 StringBuilder.toString was calling StringLatin1.newString that returned a literal "" for len == 0. After https://bugs.openjdk.org/browse/JDK-8282429 https://github.com/openjdk/jdk/commit/bab431cc120fe09be371dadef0c1caf79ec9eef4 Java 21 returns a new String object each time.  While it is minor, it still looks like a regression that effects such code paths as deserialisation.

REGRESSION : Last worked in version 17.0.10

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
new StringBuilder().toString() == ""

ACTUAL -
false

---------- BEGIN SOURCE ----------
public class Test {
    public static void main(String[] args) {
        System.out.println(new StringBuilder().toString() == "");
    }
}
---------- END SOURCE ----------

FREQUENCY : always