KAFKA-3781; Errors.exceptionName() can throw NPE

Author: Ismael Juma <ismael@juma.me.uk>

Reviewers: Grant Henke <granthenke@gmail.com>, Ewen Cheslack-Postava <ewen@confluent.io>

Closes #1476 from ijuma/kafka-3781-exception-name-npe

clients/src/main/java/org/apache/kafka/common/protocol/Errors.java

@@ -170,10 +170,10 @@ public enum Errors {
     }
 
     /**
-     * Returns the class name of the exception
+     * Returns the class name of the exception or null if this is {@code Errors.NONE}.
      */
     public String exceptionName() {
-        return exception.getClass().getName();
+        return exception == null ? null : exception.getClass().getName();
     }
 
     /**

clients/src/test/java/org/apache/kafka/common/protocol/ErrorsTest.java

@@ -77,4 +77,14 @@ public class ErrorsTest {
         assertEquals("forException should default to unknown", Errors.UNKNOWN, error);
     }
 
+    @Test
+    public void testExceptionName() {
+        String exceptionName = Errors.UNKNOWN.exceptionName();
+        assertEquals("org.apache.kafka.common.errors.UnknownServerException", exceptionName);
+        exceptionName = Errors.NONE.exceptionName();
+        assertNull(exceptionName);
+        exceptionName = Errors.INVALID_TOPIC_EXCEPTION.exceptionName();
+        assertEquals("org.apache.kafka.common.errors.InvalidTopicException", exceptionName);
+    }
+
 }