fix: Add validation to JmsConfig.Builder.brokerUrl() (#183)

Added immediate validation in the brokerUrl() setter to provide
clear error messages at the point of error instead of later during build().

Changes:
- Validate brokerUrl is not null or empty/whitespace in setter
- Throw IllegalArgumentException with clear message
- Updated existing test to expect exception from setter
- Added tests for empty and whitespace-only brokerUrl

This provides:
- Clear, immediate error messages
- Better debugging experience
- Fail-fast behavior
- Consistent API with other builder classes

Fixes #183: JmsConfig.Builder.brokerUrl() doesn't validate parameter
is non-null/empty

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: Flossy

jplatform-messaging-jms/src/main/java/org/flossware/jplatform/messaging/jms/JmsConfig.java

@@ -120,8 +120,12 @@ public static class Builder {
          *
          * @param brokerUrl the broker URL (e.g., "tcp://localhost:61616")
          * @return this builder
+         * @throws IllegalArgumentException if brokerUrl is null or empty
          */
         public Builder brokerUrl(String brokerUrl) {
+            if (brokerUrl == null || brokerUrl.trim().isEmpty()) {
+                throw new IllegalArgumentException("brokerUrl cannot be null or empty");
+            }
             this.brokerUrl = brokerUrl;
             return this;
         }

jplatform-messaging-jms/src/test/java/org/flossware/jplatform/messaging/jms/JmsConfigTest.java

@@ -46,8 +46,24 @@ void testBuilder_withDefaults() {
     void testBuilder_nullBrokerUrl() {
         JmsConfig.Builder builder = JmsConfig.builder();
 
-        assertThrows(NullPointerException.class, builder::build,
-                "Should throw NullPointerException when brokerUrl is null");
+        assertThrows(IllegalArgumentException.class, () -> builder.brokerUrl(null),
+                "Should throw IllegalArgumentException when brokerUrl is null");
+    }
+
+    @Test
+    void testBuilder_emptyBrokerUrl() {
+        JmsConfig.Builder builder = JmsConfig.builder();
+
+        assertThrows(IllegalArgumentException.class, () -> builder.brokerUrl(""),
+                "Should throw IllegalArgumentException when brokerUrl is empty");
+    }
+
+    @Test
+    void testBuilder_whitespaceBrokerUrl() {
+        JmsConfig.Builder builder = JmsConfig.builder();
+
+        assertThrows(IllegalArgumentException.class, () -> builder.brokerUrl("   "),
+                "Should throw IllegalArgumentException when brokerUrl is whitespace");
     }
 
     @Test