Numeric array data instances currently rely on ClassCastException or NullPointerException to be thrown to trigger conversion to a non-numeric array data type.

In less.js this happens often enough to show Throwable.fillInStackTrace() high in the profiler output. Even though taken by itself it's not a significant part of JDK-8019254 (all array data conversion makes less than 10% of time we spend in less.js) we should do an instanceof to avoid the exceptions.