Making Utf8StringBuilder actually throw a NotUtf8Exception in the case of an incomplete UTF8 sequence

jetty-util/src/main/java/org/eclipse/jetty/util/Utf8Appendable.java

@@ -179,6 +179,7 @@ public abstract class Utf8Appendable
         return _state == UTF8_ACCEPT;
     }
 
+    @SuppressWarnings("serial")
     public static class NotUtf8Exception extends IllegalArgumentException
     {
         public NotUtf8Exception(String reason)

jetty-util/src/main/java/org/eclipse/jetty/util/Utf8StringBuilder.java

@@ -72,6 +72,6 @@ public class Utf8StringBuilder extends Utf8Appendable
     private void checkState()
     {
         if (!isUtf8SequenceComplete())
-            throw new IllegalArgumentException("Tried to read incomplete UTF8 decoded String");
+            throw new NotUtf8Exception("Tried to read incomplete UTF8 decoded String");
     }
 }