16:41:53,742 [                main] (   internal.access.ExtractImpl) DEBUG   - com.pega.pegarules.pub.clipboard.InvalidParameterException: InvalidParameter     cannot be null  aDirectory      PropertyReference.getTopPage(ClipboardPage, PageDirectory, ClipboardPage)

com.pega.pegarules.pub.clipboard.InvalidParameterException: InvalidParameter    cannot be null  aDirectory      PropertyReference.getTopPage(ClipboardPage, PageDirectory, ClipboardPage)

        at com.pega.pegarules.data.internal.clipboard.PropertyReferenceImpl.getTopPage(PropertyReferenceImpl.java:1978)

        at com.pega.pegarules.data.internal.clipboard.PropertyReferenceImpl.getTopPage(PropertyReferenceImpl.java:1945)

        at com.pega.pegarules.data.internal.clipboard.PropertyReferenceImpl.resolveEmbeddedPages(PropertyReferenceImpl.java:1632)

        at com.pega.pegarules.data.internal.clipboard.PropertyReferenceImpl.doGet(PropertyReferenceImpl.java:1287)

        at com.pega.pegarules.data.internal.clipboard.PropertyReferenceImpl.get(PropertyReferenceImpl.java:758)

        at com.pega.pegarules.data.internal.clipboard.ClipboardPageImpl.getProperty(ClipboardPageImpl.java:886)

        at com.pega.pegarules.data.internal.clipboard.ClipboardPageImpl.getProperty(ClipboardPageImpl.java:860)

        at com.pega.pegarules.data.internal.clipboard.ClipboardPageImpl.getProperty(ClipboardPageImpl.java:850)

        at com.pega.pegarules.data.internal.clipboard.StorageStreamCommonImpl.deserializeAllBackwardPageToPageLinks(StorageStreamCommonImpl.java:1091)

        at com.pega.pegarules.data.internal.clipboard.StorageStreamCommonImpl.deserializeLink(StorageStreamCommonImpl.java:793)

        at com.pega.pegarules.data.internal.clipboard.DirectStreamContainer.addToClipboardObject(DirectStreamContainer.java:849)

        at com.pega.pegarules.data.internal.clipboard.DirectStreamContainer.applyToPage(DirectStreamContainer.java:353)

        at com.pega.pegarules.data.internal.clipboard.ClipboardPageImpl.adoptStreamForm(ClipboardPageImpl.java:667)

        at com.pega.pegarules.data.internal.clipboard.ClipboardPageImpl.adoptStreamForm(ClipboardPageImpl.java:655)

        at com.pega.pegarules.data.internal.clipboard.ClipboardPageFactoryImpl.acquireAndAdopt(ClipboardPageFactoryImpl.java:169)

        at com.pega.pegarules.data.internal.clipboard.ClipboardPageFactoryImpl$StaticHelper.acquireAndAdopt(ClipboardPageFactoryImpl.java:268)

        at com.pega.pegarules.data.external.clipboard.ClipboardPageFactory.acquireAndAdopt(ClipboardPageFactory.java:107)

        at com.pega.pegarules.data.internal.access.ExtractImpl.doExtract(ExtractImpl.java:2491)

        at com.pega.pegarules.data.internal.access.ExtractImpl.runExtract(ExtractImpl.java:1334)

        at com.pega.pegarules.data.internal.access.ExtractImpl.run(ExtractImpl.java:1105)

        at com.pega.pegarules.data.internal.access.ExtractImpl.init(ExtractImpl.java:1079)

        at com.pega.pegarules.data.internal.access.ExtractImpl.main(ExtractImpl.java:1030)

        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

        at java.lang.reflect.Method.invoke(Method.java:597)

        at com.pega.pegarules.internal.bootstrap.PRBootstrap.invokeMethod(PRBootstrap.java:349)

        at com.pega.pegarules.internal.bootstrap.PRBootstrap.invokeMethodPropagatingThrowable(PRBootstrap.java:390)

        at com.pega.pegarules.internal.bootstrap.PRBootstrap.invokeMethod(PRBootstrap.java:439)

        at com.pega.pegarules.pub.PegaRULES.main(PegaRULES.java:85)

Can you help in understanding the problem and ways to resolve it? Highly appreciate any kind of inputs on this issue.