The MXBean spec in javax.management.MXBean carefully details how types are mapped between the Java type space and the Open Type space, and how values of those types are mapped correspondingly. However, it doesn't say how null values are handled. Null values must be handled because they are used in the MXBean model already defined in Tiger for java.lang.management -- specifically, the various ThreadMXBean.getThreadInfo methods can return null values or arrays containing null values.