GH-608 'entriesObj' can be null in case the system properties are represended by a custom subclass of java.util.Properties

Author: thurka

visualvm/libs.profiler/lib.profiler.heap/src/org/graalvm/visualvm/lib/jfluid/heap/HprofProxy.java

@@ -56,7 +56,9 @@ static Properties getProperties(Instance propertiesInstance) {
             Instance map = (Instance) propertiesInstance.getValueOfField("map"); // NOI18N
             if (map != null) {
                 entriesObj = (ObjectArrayDump) map.getValueOfField("table"); // NOI18N
-                return getPropertiesFromTable(entriesObj, props, "key", "val"); // NOI18N
+                if (entriesObj != null) {
+                    return getPropertiesFromTable(entriesObj, props, "key", "val"); // NOI18N
+                }
             } else {    // old Hashtable
                 entriesObj = (ObjectArrayDump) propertiesInstance.getValueOfField("elementData"); // NOI18N
                 if (entriesObj != null) {