Bug 117925 [Intro] Misleading exception message in WelcomeEditor.init()
... it says it expects an IFileEditorInput, but it actually checks for WelcomeEditorInput. Suggested patch appended.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/ide/dialogs/WelcomeEditor.java
setLinkRanges(styledText, item.getHelpRanges());
            GridData gd = new GridData(GridData.FILL_HORIZONTAL);
            gd.horizontalSpan = 2;
            gd.horizontalIndent = HINDENT;
            gd.verticalAlignment = GridData.VERTICAL_ALIGN_BEGINNING;
            styledText.setLayoutData(gd);
            styledText.setData(item);
            addListeners(styledText);
            Label spacer = new Label(infoArea, SWT.NONE);
            spacer.setBackground(background);
            gd = new GridData(GridData.VERTICAL_ALIGN_BEGINNING);
            gd.horizontalSpan = 2;
            spacer.setLayoutData(gd);
        }
        firstText = sampleStyledText;
        
        Label imageLabel = null;
        WelcomeItem[] items = getItems();
        for (int i = 0; i < items.length; i++) {
            Label label = new Label(infoArea, SWT.NONE);
            label.setBackground(background);
            label
                    .setImage(PlatformUI
                            .getWorkbench()
                            .getSharedImages()
                            .getImage(
                                    IDEInternalWorkbenchImages.IMG_OBJS_WELCOME_ITEM));
            GridData gd = new GridData();
            gd.horizontalIndent = HINDENT;
            gd.verticalAlignment = GridData.VERTICAL_ALIGN_BEGINNING;