title: Unsupported content type when open html in Eclipse
body: <p>All, I found the default html editor in the eclipse IDE doesn't show the outlined structure. It seems IDE just treat the html as simple text, So after I installed the Web Page Editor plugin by following the answer of <a href="https://stackoverflow.com/questions/54868/what-is-the-best-html-editor-for-eclipse">https://stackoverflow.com/questions/54868/what-is-the-best-html-editor-for-eclipse</a> successfully, When I opened the html file with the <code>Web Page Editor</code>, I got a error says:</p>
  
  <p>Could not open the editor: An unexpected exception was thrown.</p>
  
  <pre><code>java.lang.NullPointerException
      at org.eclipse.wst.sse.ui.StructuredTextEditor.createModelDependentFields(StructuredTextEditor.java:1305)
      at org.eclipse.wst.sse.ui.StructuredTextEditor.update(StructuredTextEditor.java:2836)
      at org.eclipse.jst.pagedesigner.editors.HTMLEditor.sash_createAndAddDesignSourcePage(HTMLEditor.java:278)
      at org.eclipse.jst.pagedesigner.editors.HTMLEditor.createPages(HTMLEditor.java:439)
      at org.eclipse.ui.part.MultiPageEditorPart.createPartControl(MultiPageEditorPart.java:357)
      at org.eclipse.ui.internal.EditorReference.createPartHelper(EditorReference.java:662)
      at org.eclipse.ui.internal.EditorReference.createPart(EditorReference.java:462)
      at org.eclipse.ui.internal.WorkbenchPartReference.getPart(WorkbenchPartReference.java:595)
      at org.eclipse.ui.internal.EditorReference.getEditor(EditorReference.java:286)
      at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditorBatched(WorkbenchPage.java:2857)
      at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditor(WorkbenchPage.java:2762)
      at org.eclipse.ui.internal.WorkbenchPage.access$11(WorkbenchPage.java:2754)
      at org.eclipse.ui.internal.WorkbenchPage$10.run(WorkbenchPage.java:2705)
      at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
      at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2701)
      at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:2685)
      at org.eclipse.ui.actions.OpenWithMenu.openEditor(OpenWithMenu.java:344)
      at org.eclipse.ui.actions.OpenWithMenu$2.handleEvent(OpenWithMenu.java:192)
      at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
      at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1003)
      at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3910)
      at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3503)
      at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2405)
      at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2369)
      at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2221)
      at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:500)
      at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
      at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:493)
      at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
      at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:113)
      at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:194)
      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:368)
      at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:601)
      at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:559)
      at org.eclipse.equinox.launcher.Main.basicRun(Main.java:514)
      at org.eclipse.equinox.launcher.Main.run(Main.java:1311)
      at org.eclipse.equinox.launcher.Main.main(Main.java:1287)
  </code></pre>
  
  <p>And also pop up an error says:</p>
  
  <pre><code>Unsupported content type in editor.
  To associate file extension with a supported content type,
  Please see Content Type Preference Page.
  </code></pre>
  
  <p>And I still checked the <code>Content Type Preference Page</code>. Below is the setting .please review it .
  <img src="https://i.stack.imgur.com/2A1Vk.png" alt="enter image description here"></p>
  
  <p>Is there anyone ever encountered this problem before? thanks.</p>