FULL PRODUCT VERSION :
java version "9"
Java(TM) SE Runtime Environment (build 9+178)
Java HotSpot(TM) 64-Bit Server VM (build 9+178, mixed mode)

A DESCRIPTION OF THE PROBLEM :
When using DirectExecutionControl, then exceptions thrown with null messages cause NullPointerExceptions to be thrown in Eval:translateExceptionMessage because it calls equals on the message. The default execution control doesn't because it converts null messages into the empty string.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run main method of given class.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Program should complete normally.
ACTUAL -
NullPointerException is thrown.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "main" java.lang.NullPointerException
at jdk.jshell/jdk.jshell.Eval.translateExceptionMessage(Eval.java:763)
at jdk.jshell/jdk.jshell.Eval.declare(Eval.java:553)
at jdk.jshell/jdk.jshell.Eval.eval(Eval.java:118)
at jdk.jshell/jdk.jshell.JShell.eval(JShell.java:493)
at Main.main(Main.java:23)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.HashMap;
import java.util.Map;

import jdk.jshell.JShell;
import jdk.jshell.execution.DirectExecutionControl;
import jdk.jshell.spi.ExecutionControl;
import jdk.jshell.spi.ExecutionControlProvider;
import jdk.jshell.spi.ExecutionEnv;

public class Main {
public static void main(String[] args) {
JShell jshell = JShell.builder().executionEngine(new ExecutionControlProvider() {
public ExecutionControl generate(ExecutionEnv env, Map<String, String> param) throws Throwable {
return new DirectExecutionControl();
}

public String name() {
return "Name";
}

}, new HashMap<>()).build();

jshell.eval("throw new java.io.IOException();");
}
}
---------- END SOURCE ----------