Integration of JDK-8254082 introduced regression. Running the following code

public class Test {
    public static void main(String... args) {
        new StringBuffer("abc").insert(0, "def", 1, 3);
    }
}

now leads to

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: arraycopy: last source index 4 out of bounds for byte[3]
at java.base/java.lang.System.arraycopy(Native Method)
at java.base/java.lang.String.getBytes(String.java:3624)
at java.base/java.lang.AbstractStringBuilder.putStringAt(AbstractStringBuilder.java:1720)
at java.base/java.lang.AbstractStringBuilder.insert(AbstractStringBuilder.java:1301)
at java.base/java.lang.StringBuffer.insert(StringBuffer.java:588)
at Test.main(Test.java:3)

Please see the specification
https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/StringBuffer.html#insert(int,java.lang.CharSequence,int,int)
to check input data validity