Merge branch '2.1'

core/src/main/java/org/apache/accumulo/core/conf/AccumuloConfiguration.java

@@ -469,6 +469,12 @@ public T derive() {
       if (rc == null || rc.count != uc) {
         T newObj = converter.apply(AccumuloConfiguration.this);
 
+        if (newObj == null) {
+          // The converter should not return a null value and the Deriver
+          // should not store and return a null value.
+          throw new IllegalStateException("Deriver returned a null value");
+        }
+
         // very important to record the update count that was obtained before recomputing.
         RefCount<T> nrc = new RefCount<>(uc, newObj);
 
@@ -507,6 +513,7 @@ public interface Deriver<T> {
    *        this function will be kept and called by the returned deriver.
    * @return The returned supplier will automatically re-derive the object any time this
    *         configuration changes. When configuration is not changing, the same object is returned.
+   * @throws IllegalStateException When a null return value is returned by the converter.
    *
    */
   public <T> Deriver<T> newDeriver(Function<AccumuloConfiguration,T> converter) {

core/src/main/java/org/apache/accumulo/core/conf/ConfigurationTypeHelper.java

@@ -176,8 +176,9 @@ public static <T> T getClassInstance(String context, String clazzName, Class<T>
       log.error("Failed to load class {} in classloader context {}", clazzName, context, e);
     }
 
-    if (instance == null && defaultInstance != null) {
-      log.info("Using default class {}", defaultInstance.getClass().getName());
+    if (instance == null) {
+      log.info("Using default class ({})",
+          defaultInstance == null ? null : defaultInstance.getClass().getName());
       instance = defaultInstance;
     }
     return instance;

core/src/main/java/org/apache/accumulo/core/conf/Property.java

@@ -25,6 +25,7 @@
 import java.util.EnumSet;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.Objects;
 import java.util.function.Predicate;
 
 import org.apache.accumulo.core.classloader.ClassLoaderUtil;
@@ -1609,6 +1610,9 @@ public static boolean isClassProperty(String key) {
    */
   public static <T> T createTableInstanceFromPropertyName(AccumuloConfiguration conf,
       Property property, Class<T> base, T defaultInstance) {
+    Objects.requireNonNull(conf, "configuration cannot be null");
+    Objects.requireNonNull(property, "property cannot be null");
+    Objects.requireNonNull(base, "base class cannot be null");
     String clazzName = conf.get(property);
     String context = ClassLoaderUtil.tableContext(conf);
     return ConfigurationTypeHelper.getClassInstance(context, clazzName, base, defaultInstance);

server/base/src/main/java/org/apache/accumulo/server/conf/TableConfiguration.java

@@ -24,6 +24,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Objects;
 import java.util.stream.Collectors;
 
 import org.apache.accumulo.core.classloader.ClassLoaderUtil;
@@ -145,6 +146,8 @@ private static ScanDispatcher createScanDispatcher(AccumuloConfiguration conf,
       ServerContext context, TableId tableId) {
     ScanDispatcher newDispatcher = Property.createTableInstanceFromPropertyName(conf,
         Property.TABLE_SCAN_DISPATCHER, ScanDispatcher.class, null);
+    Objects.requireNonNull(newDispatcher, "Class specified in property "
+        + Property.TABLE_SCAN_DISPATCHER.getKey() + " was not returned.");
 
     Map<String,String> opts =
         conf.getAllPropertiesWithPrefixStripped(Property.TABLE_SCAN_DISPATCHER_OPTS);
@@ -177,14 +180,8 @@ private static CompactionDispatcher createCompactionDispatcher(AccumuloConfigura
 
     CompactionDispatcher newDispatcher = Property.createTableInstanceFromPropertyName(conf,
         Property.TABLE_COMPACTION_DISPATCHER, CompactionDispatcher.class, null);
-
-    if (newDispatcher == null) {
-      // return early to prevent NPE
-      log.error(
-          "Null returned for compaction dispatcher for table: {}. Did not return default value, check server log.",
-          tableId);
-      return null;
-    }
+    Objects.requireNonNull(newDispatcher, "Class specified in property "
+        + Property.TABLE_COMPACTION_DISPATCHER.getKey() + " was not returned.");
 
     Map<String,String> opts =
         conf.getAllPropertiesWithPrefixStripped(Property.TABLE_COMPACTION_DISPATCHER_OPTS);