java.lang.NullPointerException
	at org.graalvm.visualvm.lib.jfluid.heap.LongBuffer.startReading(LongBuffer.java:138)
	at org.graalvm.visualvm.lib.jfluid.heap.TreeObject.switchBuffers(TreeObject.java:193)
	at org.graalvm.visualvm.lib.jfluid.heap.TreeObject.computeTrees(TreeObject.java:84)
	at org.graalvm.visualvm.lib.jfluid.heap.HprofHeap.computeRetainedSize(HprofHeap.java:761)
	at org.graalvm.visualvm.lib.jfluid.heap.HprofHeap.getRetainedSize(HprofHeap.java:457)
	at org.graalvm.visualvm.lib.jfluid.heap.InstanceDump.getRetainedSize(InstanceDump.java:119)
	at org.graalvm.visualvm.heapviewer.utils.HeapOperations$3.run(HeapOperations.java:209)

To Reproduce
Steps to reproduce the behavior:

Open heap dump
Compute GC roots
Close VisualVM
Open the same heap dump
Compute retained sizes
NPE

VisualVM log
messages.log