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
int ellipseWidth = gc.textExtent(ellipsis, SWT.DRAW_MNEMONIC).x;
                int length = text.length();
                int end = length - 1;
                while (end > 0) {
                    text = text.substring(0, end);
                    int l1 = gc.textExtent(text, SWT.DRAW_MNEMONIC).x;
                    if (l1 + ellipseWidth <= width) {
                        return text + ellipsis;
                    }
                    end--;
                }
                return text + ellipsis;
            }
        };
        JFaceColors.setColors(messageLabel, foreground, background);
        messageLabel.setText(getBannerTitle());
        messageLabel.setFont(JFaceResources.getHeaderFont());
        final IPropertyChangeListener fontListener = new IPropertyChangeListener() {
            public void propertyChange(PropertyChangeEvent event) {
                if (JFaceResources.HEADER_FONT.equals(event.getProperty())) {
                    messageLabel.setFont(JFaceResources.getHeaderFont());
                }
            }
        };
        messageLabel.addDisposeListener(new DisposeListener() {
            public void widgetDisposed(DisposeEvent event) {
                JFaceResources.getFontRegistry().removeListener(fontListener);
            }
        });
        JFaceResources.getFontRegistry().addListener(fontListener);