When you get the properties of image, provide an alternative path in case there is no image.
String image = properties.get("your_image_path", "/some/path/mysitelogo.jpg"); %><div class="image"><img src="<%= image%>" alt="Alternate text" ></div><%
This will return the default value to your image (after you correct the path). Since the ValueMap will automatically return the default value if the retrieved value is null, you no longer have to do the null check.