Null Pointer Exception when trying to export Extension Projects #62

A Null Pointer Exception arises under two conditions:

1. There is no Extension project to be exported
2. If no project exists under the Package Explorer (or no Extension project is selected under the Package Explorer) and you go File->Export->LibreOffice package.

!ENTRY org.eclipse.ui 4 0 2018-02-28 17:44:34.662
!MESSAGE Unhandled event loop exception
!STACK 0
java.lang.NullPointerException
at org.libreoffice.ide.eclipse.core.gui.PackageContentSelector.getDefaultContent(PackageContentSelector.java:145)
at org.libreoffice.ide.eclipse.core.gui.PackageContentSelector.loadDefaults(PackageContentSelector.java:109)
at org.libreoffice.ide.eclipse.core.wizards.pages.UnoPackageExportPage.loadData(UnoPackageExportPage.java:149)
at org.libreoffice.ide.eclipse.core.wizards.pages.UnoPackageExportPage.createControl(UnoPackageExportPage.java:129)
at org.eclipse.jface.wizard.Wizard.createPageControls(Wizard.java:175)
at org.eclipse.jface.wizard.WizardDialog.createPageControls(WizardDialog.java:696)
at org.eclipse.jface.wizard.WizardDialog.setWizard(WizardDialog.java:1144)
at org.eclipse.jface.wizard.WizardDialog.updateForPage(WizardDialog.java:1197)
at org.eclipse.jface.wizard.WizardDialog.lambda$2(WizardDialog.java:1185)
at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
at org.eclipse.jface.wizard.WizardDialog.showPage(WizardDialog.java:1185)
at org.eclipse.jface.wizard.WizardDialog.nextPressed(WizardDialog.java:876)
at org.eclipse.jface.wizard.WizardDialog.buttonPressed(WizardDialog.java:419)
at org.eclipse.jface.dialogs.Dialog$2.widgetSelected(Dialog.java:618)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:249)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)