ChronicleMapBuilder.defaultValue() shouldn't be null because ChronicleMap generally doesn't support neither null key nor null values

src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java

@@ -940,10 +940,10 @@ public final class ChronicleMapBuilder<K, V> implements Cloneable,
      * @see #prepareDefaultValueBytes(PrepareValueBytes)
      */
     public ChronicleMapBuilder<K, V> defaultValue(V defaultValue) {
+        if (defaultValue == null)
+            throw new IllegalArgumentException("default ChronicleMap value couldn't be null");
         this.defaultValue = defaultValue;
         this.defaultValueProvider = null;
-        if (defaultValue == null)
-            defaultValueProvider = NullValueProvider.INSTANCE;
         this.prepareValueBytes = null;
         return this;
     }

src/main/java/net/openhft/chronicle/map/NullValueProvider.java

@@ -1,28 +0,0 @@
-/*
- * Copyright 2014 Higher Frequency Trading
- *
- * http://www.higherfrequencytrading.com
- *
- * Licensed 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 net.openhft.chronicle.map;
-
-enum NullValueProvider implements DefaultValueProvider {
-    INSTANCE;
-
-    @Override
-    public Object get(Object key) {
-        return null;
-    }
-}