give UserType.replace() a sensible default impl that's essentially always correct

documentation/src/test/java/org/hibernate/userguide/mapping/basic/bitset/BitSetUserType.java

@@ -94,11 +94,5 @@ public class BitSetUserType implements UserType<BitSet> {
     public BitSet assemble(Serializable cached, Object owner)  {
         return deepCopy((BitSet) cached);
     }
-
-    @Override
-    public BitSet replace(BitSet original, BitSet target, Object owner)
-			throws HibernateException {
-        return deepCopy(original);
-    }
 }
 //end::basic-custom-type-BitSetUserType-example[]

hibernate-core/src/main/java/org/hibernate/usertype/BaseUserTypeSupport.java

@@ -112,9 +112,4 @@ public abstract class BaseUserTypeSupport<T> implements UserType<T> {
 	public T assemble(Serializable cached, Object owner) throws HibernateException {
 		return javaType().getMutabilityPlan().assemble( cached, null );
 	}
-
-	@Override
-	public T replace(T original, T target, Object owner) throws HibernateException {
-		return deepCopy( original );
-	}
 }

hibernate-core/src/main/java/org/hibernate/usertype/StaticUserTypeSupport.java

@@ -158,10 +158,4 @@ public class StaticUserTypeSupport<T> implements UserType<T> {
 	public T assemble(Serializable cached, Object owner) throws HibernateException {
 		return javaType.getMutabilityPlan().assemble( cached, null );
 	}
-
-	@Override
-	public T replace(T original, T target, Object owner) throws HibernateException {
-		return deepCopy( original );
-	}
-
 }

hibernate-core/src/main/java/org/hibernate/usertype/UserType.java

@@ -102,11 +102,6 @@ import org.hibernate.type.spi.TypeConfiguration;
  *     public Period assemble(Serializable cached, Object owner) {
  *         return (Period) cached; //Period is immutable
  *     }
- *
- *     @Override
- *     public Period replace(Period detached, Period managed, Object owner) {
- *         return detached;
- *     }
  * }
  * </pre>
  * <p>
@@ -395,7 +390,9 @@ public interface UserType<J> {
 	 *
 	 * @see org.hibernate.Session#merge(Object)
 	 */
-	J replace(J detached, J managed, Object owner);
+	default J replace(J detached, J managed, Object owner) {
+		return deepCopy( detached );
+	}
 
 	/**
 	 * The default column length, for use in DDL generation.