fix: no empty first line in log (#22523) (#22539)

Added message to not log
with "" and throwable.

fixes #22522

Co-authored-by: caalador <mikael.grankvist@vaadin.com>

Author: vaadin-bot

flow-server/src/main/java/com/vaadin/flow/server/DefaultErrorHandler.java

@@ -93,7 +93,8 @@ public void error(ErrorEvent event) {
             Marker marker = MarkerFactory.getMarker("INVALID_LOCATION");
             if (throwable instanceof InvalidLocationException) {
                 if (getLogger().isWarnEnabled(marker)) {
-                    getLogger().warn(marker, "", throwable);
+                    getLogger().warn(marker, "Invalid location: {}",
+                            throwable.getMessage(), throwable);
                 }
             } else {
                 if (routeConfigurationExceptions
@@ -102,7 +103,8 @@ public void error(ErrorEvent event) {
                     getLogger().error(throwable.getMessage());
                 } else {
                     // print the error on console
-                    getLogger().error("", throwable);
+                    getLogger().error("Unexpected error: {}",
+                            throwable.getMessage(), throwable);
                 }
             }
         }

flow-server/src/test/java/com/vaadin/flow/server/DefaultErrorHandlerTest.java

@@ -60,11 +60,11 @@ public void error_acceptedException_errorHandled() {
 
         Throwable throwable = new RuntimeException();
         errorHandler.error(new ErrorEvent(throwable));
-        Mockito.verify(logger).error("", throwable);
+        Mockito.verify(logger).error("Unexpected error: {}", null, throwable);
 
         throwable = new IllegalArgumentException();
         errorHandler.error(new ErrorEvent(throwable));
-        Mockito.verify(logger).error("", throwable);
+        Mockito.verify(logger).error("Unexpected error: {}", null, throwable);
     }
 
     @Test
@@ -90,7 +90,7 @@ public void error_subclassOfIgnoredException_errorHandled() {
 
         Throwable throwable = new MalformedURLException();
         errorHandler.error(new ErrorEvent(throwable));
-        Mockito.verify(logger).error("", throwable);
+        Mockito.verify(logger).error("Unexpected error: {}", null, throwable);
     }
 
     @Test
@@ -105,23 +105,24 @@ public void error_loggerAtDebugLevel_errorHandled() {
 
         Throwable throwable = new RuntimeException();
         errorHandler.error(new ErrorEvent(throwable));
-        Mockito.verify(logger).error("", throwable);
+        Mockito.verify(logger).error("Unexpected error: {}", null, throwable);
 
         throwable = new IOException();
         errorHandler.error(new ErrorEvent(throwable));
-        Mockito.verify(logger).error("", throwable);
+        Mockito.verify(logger).error("Unexpected error: {}", null, throwable);
 
         throwable = new MalformedURLException();
         errorHandler.error(new ErrorEvent(throwable));
-        Mockito.verify(logger).error("", throwable);
+        Mockito.verify(logger).error("Unexpected error: {}", null, throwable);
 
         throwable = new InnerException();
         errorHandler.error(new ErrorEvent(throwable));
-        Mockito.verify(logger).error("", throwable);
+        Mockito.verify(logger).error("Unexpected error: {}", null, throwable);
 
         throwable = new UncheckedIOException(new IOException());
         errorHandler.error(new ErrorEvent(throwable));
-        Mockito.verify(logger).error("", throwable);
+        Mockito.verify(logger).error("Unexpected error: {}",
+                "java.io.IOException", throwable);
     }
 
     public static class InnerException extends Exception {