MINOR: Add error message to setMaxPendingMessagesAcrossPartitions (ap…

…ache#10709)

### Motivation
When maxPendingMessagesAcrossPartitions is less than maxPendingMessages, an error message will be thrown: null

### Modifications
return "maxPendingMessagesAcrossPartitions needs to be >= maxPendingMessages" instead

pulsar-client/src/main/java/org/apache/pulsar/client/impl/conf/ProducerConfigurationData.java

@@ -136,7 +136,8 @@ public void setMaxPendingMessages(int maxPendingMessages) {
     }
 
     public void setMaxPendingMessagesAcrossPartitions(int maxPendingMessagesAcrossPartitions) {
-        checkArgument(maxPendingMessagesAcrossPartitions >= maxPendingMessages);
+        checkArgument(maxPendingMessagesAcrossPartitions >= maxPendingMessages,
+                "maxPendingMessagesAcrossPartitions needs to be >= maxPendingMessages");
         this.maxPendingMessagesAcrossPartitions = maxPendingMessagesAcrossPartitions;
     }
 

pulsar-client/src/test/java/org/apache/pulsar/client/impl/ProducerBuilderImplTest.java

@@ -343,6 +343,11 @@ public void testProducerBuilderImplWhenMaxPendingMessagesAcrossPartitionsPropert
         producerBuilderImpl.maxPendingMessagesAcrossPartitions(999);
     }
 
+    @Test(expectedExceptions = IllegalArgumentException.class, expectedExceptionsMessageRegExp = "maxPendingMessagesAcrossPartitions needs to be >= maxPendingMessages")
+    public void testProducerBuilderImplWhenMaxPendingMessagesAcrossPartitionsPropertyIsInvalidErrorMessages() {
+        producerBuilderImpl.maxPendingMessagesAcrossPartitions(999);
+    }
+
     @Test
     public void testProducerBuilderImplWhenNumericPropertiesAreValid() {
         producerBuilderImpl.batchingMaxPublishDelay(1, TimeUnit.SECONDS);