SLING-8907 - Journal distribution agents with empty names are invalid (#87)

diff --git a/src/main/java/org/apache/sling/distribution/journal/impl/publisher/DistributionPublisher.java b/src/main/java/org/apache/sling/distribution/journal/impl/publisher/DistributionPublisher.java
index e4adb8a..8ee0d6f 100644
--- a/src/main/java/org/apache/sling/distribution/journal/impl/publisher/DistributionPublisher.java
+++ b/src/main/java/org/apache/sling/distribution/journal/impl/publisher/DistributionPublisher.java
@@ -25,6 +25,7 @@
 import static org.apache.sling.distribution.DistributionRequestType.DELETE;
 import static org.apache.sling.distribution.DistributionRequestType.TEST;
 import static org.apache.sling.distribution.journal.shared.DistributionMetricsService.timed;
+import static org.apache.sling.distribution.journal.shared.Strings.requireNotBlank;
 
 import java.io.Closeable;
 import java.util.Collections;
@@ -152,7 +153,7 @@
     public void activate(PublisherConfiguration config, BundleContext context) {
         requireNonNull(factory);
         requireNonNull(distributionMetricsService);
-        pubAgentName = requireNonNull(config.name());
+        pubAgentName = requireNotBlank(config.name());
 
         queuedTimeout = config.queuedTimeout();
 
diff --git a/src/main/java/org/apache/sling/distribution/journal/impl/subscriber/DistributionSubscriber.java b/src/main/java/org/apache/sling/distribution/journal/impl/subscriber/DistributionSubscriber.java
index 9e676d9..9460068 100644
--- a/src/main/java/org/apache/sling/distribution/journal/impl/subscriber/DistributionSubscriber.java
+++ b/src/main/java/org/apache/sling/distribution/journal/impl/subscriber/DistributionSubscriber.java
@@ -25,6 +25,7 @@
 import static java.util.stream.Collectors.toSet;
 import static org.apache.sling.distribution.journal.RunnableUtil.startBackgroundThread;
 import static org.apache.sling.distribution.journal.shared.Delay.exponential;
+import static org.apache.sling.distribution.journal.shared.Strings.requireNotBlank;
 
 import java.io.Closeable;
 import java.io.IOException;
@@ -157,7 +158,7 @@
     @Activate
     public void activate(SubscriberConfiguration config, BundleContext context, Map<String, Object> properties) {
         String subSlingId = requireNonNull(slingSettings.getSlingId());
-        subAgentName = requireNonNull(config.name());
+        subAgentName = requireNotBlank(config.name());
         requireNonNull(config);
         requireNonNull(context);
         requireNonNull(packageBuilder);
diff --git a/src/main/java/org/apache/sling/distribution/journal/shared/Strings.java b/src/main/java/org/apache/sling/distribution/journal/shared/Strings.java
new file mode 100644
index 0000000..92aabcb
--- /dev/null
+++ b/src/main/java/org/apache/sling/distribution/journal/shared/Strings.java
@@ -0,0 +1,34 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.sling.distribution.journal.shared;
+
+import org.apache.commons.lang3.StringUtils;
+
+public final class Strings {
+
+    private Strings() {}
+
+    public static String requireNotBlank(String value) {
+        if (StringUtils.isBlank(value)) {
+            throw new IllegalArgumentException("Can't be blank");
+        }
+        return value;
+    }
+
+}
diff --git a/src/test/java/org/apache/sling/distribution/journal/shared/StringsTest.java b/src/test/java/org/apache/sling/distribution/journal/shared/StringsTest.java
new file mode 100644
index 0000000..62b3f57
--- /dev/null
+++ b/src/test/java/org/apache/sling/distribution/journal/shared/StringsTest.java
@@ -0,0 +1,48 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.sling.distribution.journal.shared;
+
+import org.junit.Test;
+
+import static org.apache.sling.distribution.journal.shared.Strings.requireNotBlank;
+import static org.junit.Assert.assertEquals;
+
+public class StringsTest {
+
+    @Test
+    public void requireNotBlankTest() {
+        String value = "a";
+        assertEquals(value, requireNotBlank(value));
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void requireNotBlankFailedTest1() {
+        requireNotBlank(null);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void requireNotBlankFailedTest2() {
+        requireNotBlank("");
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void requireNotBlankFailedTest3() {
+        requireNotBlank(" ");
+    }
+}
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