java.lang.NullPointerException
   at org.netbeans.modules.erd.io.DocumentLoad.getChildNode(DocumentLoad.java:179)
   at org.netbeans.modules.erd.io.DocumentLoad.load(DocumentLoad.java:84)
   at org.netbeans.modules.erd.model.DocumentSerializer$1.run(DocumentSerializer.java:78)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1454)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2036)