reverted back to allow acquireUsing to be passsed a NULL value

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

@@ -173,7 +173,7 @@ public interface ChronicleMap<K, V> extends ConcurrentMap<K, V>, ChronicleHash {
      * @return value to which the given key is mapping after this call, either found or created
      * @see #getUsing(Object, Object)
      */
-    V acquireUsing(@NotNull K key, @NotNull V usingValue);
+    V acquireUsing(@NotNull K key, V usingValue);
 
 
     @NotNull

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

@@ -391,7 +391,7 @@ class StatelessChronicleMap<K, V> implements ChronicleMap<K, V>, Closeable {
     }
 
 
-    public synchronized V acquireUsing(@NotNull K key, @NotNull V usingValue) {
+    public synchronized V acquireUsing(@NotNull K key,  V usingValue) {
         throw new UnsupportedOperationException("acquireUsing() is not supported for stateless " +
                 "clients");
     }

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

@@ -383,7 +383,7 @@ class VanillaChronicleMap<K, KI, MKI extends MetaBytesInterop<K, KI>,
 
 
     @Override
-    public V acquireUsing(@NotNull K key, @NotNull V usingValue) {
+    public V acquireUsing(@NotNull K key, V usingValue) {
 
         try (WriteContext<K, V> kvContext =
                      lookupUsing(key, usingValue, LockType.WRITE_LOCK, false)) {
@@ -856,7 +856,7 @@ class VanillaChronicleMap<K, KI, MKI extends MetaBytesInterop<K, KI>,
         }
 
         V acquireWithoutLock(ThreadLocalCopies copies, MKI metaKeyInterop, KI keyInterop, K key, V usingValue,
-                   long hash2, boolean create) {
+                             long hash2, boolean create) {
             long keySize = metaKeyInterop.size(keyInterop, key);
             MultiStoreBytes entry = acquireTmpBytes();
             long offset = searchKey(keyInterop, metaKeyInterop, key, keySize, hash2, entry,