ClassNotFoundException when running on Java 8 on an IBM J9 VM within WebSphere

Customer is getting error:
java.lang.ClassNotFoundException: com.sun.management.HotSpotDiagnosticMXBean when using the SpaceProxyConfigurer running on Java 8 on an IBM J9 VM within WebSphere.

I can see in our open source code repository where the HotSpotDiagnosticMXBean was added.

https://github.com/xap/xap/blob/5e2a2f9e9f2638b0859912464783577d89ec3a05/xap-core/xap-common/src/main/java/com/gigaspaces/internal/jvm/JavaUtils.java

(It also can be found in com/gigaspaces/internal/dump/heap/HeapDumpProcessor.java)

It seems this change was added prior to 15.5 in JIRA GS-14028.

According to this documentation I found on IBM's website, they have their own method for generating a heap dump that doesn't use HotSpotDiagnosticMXBean.
See:
https://publib.boulder.ibm.com/httpserv/cookbook/Applications.html