title: How to fix the nullpointerexception that comes up in Eclipse when trying to open an Android XML file?
body: <p>Since I updated the ADT plugin to v1.21 in Eclipse, I can no longer easily open any XML layout files in my Android project. As soon as, I click on the file, It throws NullPointerException. Here are the stack traces from the error log:</p>
  
  <pre><code>java.lang.NullPointerException
      at com.android.ide.eclipse.adt.internal.editors.common.CommonMatchingStrategy.matches(CommonMatchingStrategy.java:59)
      at org.eclipse.ui.internal.WorkbenchPage.checkEditor(WorkbenchPage.java:2254)
      at org.eclipse.ui.internal.WorkbenchPage.findEditors(WorkbenchPage.java:2223)
      at org.eclipse.ui.internal.WorkbenchPage.findEditor(WorkbenchPage.java:2205)
      at org.eclipse.jdt.internal.ui.javaeditor.EditorUtility.isOpenInEditor(EditorUtility.java:131)
      at org.eclipse.jdt.internal.ui.packageview.PackageExplorerPart.linkToEditor(PackageExplorerPart.java:929)
      at org.eclipse.jdt.internal.ui.packageview.PackageExplorerPart.access$2(PackageExplorerPart.java:926)
      at org.eclipse.jdt.internal.ui.packageview.PackageExplorerPart$4.linkToEditor(PackageExplorerPart.java:533)
      at org.eclipse.ui.OpenAndLinkWithEditorHelper$InternalListener.selectionChanged(OpenAndLinkWithEditorHelper.java:57)
      at org.eclipse.jface.viewers.StructuredViewer$3.run(StructuredViewer.java:888)
      at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
      at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:49)
      at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:175)
      at org.eclipse.jface.viewers.StructuredViewer.firePostSelectionChanged(StructuredViewer.java:886)
      at org.eclipse.jface.viewers.StructuredViewer.handlePostSelect(StructuredViewer.java:1226)
      at org.eclipse.jface.viewers.StructuredViewer$5.widgetSelected(StructuredViewer.java:1251)
      at org.eclipse.jface.util.OpenStrategy.firePostSelectionEvent(OpenStrategy.java:262)
      at org.eclipse.jface.util.OpenStrategy.access$5(OpenStrategy.java:256)
      at org.eclipse.jface.util.OpenStrategy$3.run(OpenStrategy.java:433)
      at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
      at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:135)
      at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:4144)
      at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3761)
      at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1029)
      at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
      at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:923)
      at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:86)
      at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:588)
      at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
      at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:543)
      at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
      at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:124)
      at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
      at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
      at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
      at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:353)
      at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:180)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
      at java.lang.reflect.Method.invoke(Unknown Source)
      at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:629)
      at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584)
      at org.eclipse.equinox.launcher.Main.run(Main.java:1438)
      at org.eclipse.equinox.launcher.Main.main(Main.java:1414)
  </code></pre>
  
  <p>I can open the file if I right-click on it, and tell it t open with the Legacy Android Layout editor, but it's obviously not good solution. I tried going into Eclipse preferences, and made sure that the file associations for the XML files are set correctly.</p>