HADOOP-14459. SerializationFactory shouldn't throw a NullPointerException if the serializations list is not defined

(Contributed by Nandor Kollar via Daniel Templeton)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/serializer/SerializationFactory.java

@@ -55,18 +55,12 @@ public class SerializationFactory extends Configured {
    */
   public SerializationFactory(Configuration conf) {
     super(conf);
-    if (conf.get(CommonConfigurationKeys.IO_SERIALIZATIONS_KEY).equals("")) {
-      LOG.warn("Serialization for various data types may not be available. Please configure "
-          + CommonConfigurationKeys.IO_SERIALIZATIONS_KEY
-          + " properly to have serialization support (it is currently not set).");
-    } else {
-      for (String serializerName : conf.getTrimmedStrings(
-          CommonConfigurationKeys.IO_SERIALIZATIONS_KEY, new String[] {
-              WritableSerialization.class.getName(),
-              AvroSpecificSerialization.class.getName(),
-              AvroReflectSerialization.class.getName() })) {
-        add(conf, serializerName);
-      }
+    for (String serializerName : conf.getTrimmedStrings(
+            CommonConfigurationKeys.IO_SERIALIZATIONS_KEY,
+            new String[]{WritableSerialization.class.getName(),
+                    AvroSpecificSerialization.class.getName(),
+                    AvroReflectSerialization.class.getName()})) {
+      add(conf, serializerName);
     }
   }
 

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/io/serializer/TestSerializationFactory.java

@@ -51,6 +51,19 @@ public class TestSerializationFactory {
     SerializationFactory factory = new SerializationFactory(conf);
   }
 
+  /**
+   * Test the case when {@code IO_SERIALIZATIONS_KEY}
+   * is not set at all, because something unset this key.
+   * This shouldn't result in any error, the defaults present
+   * in construction should be used in this case.
+   */
+  @Test
+  public void testSerializationKeyIsUnset() {
+    Configuration conf = new Configuration();
+    conf.unset(CommonConfigurationKeys.IO_SERIALIZATIONS_KEY);
+    SerializationFactory factory = new SerializationFactory(conf);
+  }
+
   @Test
   public void testSerializationKeyIsInvalid() {
     Configuration conf = new Configuration();