Fix NPE when serializing an Exception with a null message (#45)

Author: felixbarny

ecs-logging-core/src/main/java/co/elastic/logging/EcsJsonSerializer.java

@@ -159,9 +159,13 @@ public static void serializeException(StringBuilder builder, Throwable thrown, b
             builder.append("\"error.type\":\"");
             JsonUtils.quoteAsString(thrown.getClass().getName(), builder);
             builder.append("\",");
-            builder.append("\"error.message\":\"");
-            JsonUtils.quoteAsString(thrown.getMessage(), builder);
-            builder.append("\",");
+
+            String message = thrown.getMessage();
+            if (message != null) {
+                builder.append("\"error.message\":\"");
+                JsonUtils.quoteAsString(message, builder);
+                builder.append("\",");
+            }
             if (stackTraceAsArray) {
                 builder.append("\"error.stack_trace\":[").append(NEW_LINE);
                 formatThrowableAsArray(builder, thrown);

ecs-logging-core/src/test/java/co/elastic/logging/AbstractEcsLoggingTest.java

@@ -103,6 +103,13 @@ void testLogException() throws Exception {
         assertThat(stackTrace).contains("at co.elastic.logging.AbstractEcsLoggingTest.testLogException");
     }
 
+    @Test
+    void testLogExceptionNullMessage() throws Exception {
+        error("test", new RuntimeException());
+        assertThat(getLastLogLine().get("error.message")).isNull();
+        assertThat(getLastLogLine().get("error.type").textValue()).isEqualTo(RuntimeException.class.getName());
+    }
+
     @Test
     void testLogOrigin() throws Exception {
         debug("test");