Bug 300855 Do not allow Path Variables with empty location
HEAD I'm able to create a path variable without location. Next, when I want to edit the variable, Edit Variable dialog opens with error saying "You must provide a file or folder path as variable value.". I guess I should not be able to create such variable in the first place.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/ide/dialogs/PathVariableDialog.java
}
    /**
     * Creates and configures this dialog's main composite.
     * 
     * @param parentComposite parent's composite
     * @return this dialog's main composite
     */
    private Composite createComposite(Composite parentComposite) {
        
        Composite contents = new Composite(parentComposite, SWT.NONE);
        contents.setLayout(new GridLayout(3, false));
        contents.setLayoutData(new GridData(GridData.FILL_BOTH));
        if (operationMode == NEW_VARIABLE)
            setTitle(IDEWorkbenchMessages.PathVariableDialog_dialogTitle_newVariable);
        else if (operationMode == EXISTING_VARIABLE)
            setTitle(IDEWorkbenchMessages.PathVariableDialog_dialogTitle_existingVariable);
        else
            setTitle(IDEWorkbenchMessages.PathVariableDialog_dialogTitle_editLinkLocation);
        setMessage(standardMessage);
        return contents;
    }
    /**
     * Creates widgets for this dialog.
     * 
     * @param contents the parent composite where to create widgets
     */
    private void createWidgets(Composite contents) {
        String nameLabelText = IDEWorkbenchMessages.PathVariableDialog_variableName;
        String valueLabelText = IDEWorkbenchMessages.PathVariableDialog_variableValue;
        String resolvedValueLabelText = IDEWorkbenchMessages.PathVariableDialog_variableResolvedValue;