Apply suggestions from code review

Author: hazzik

src/NHibernate/Type/AbstractStringType.cs

@@ -67,7 +67,7 @@ public override void Set(DbCommand cmd, object value, int index, ISessionImpleme
 			// set the parameter value before the size check, since ODBC changes the size automatically
 			parameter.Value = value;
 
-			if (parameter.Size > 0 && value != null && ((string) value).Length > parameter.Size)
+			if (parameter.Size > 0 && ((string)value).Length > parameter.Size)
 				throw new HibernateException("The length of the string value exceeds the length configured in the mapping/parameter.");
 		}