DefaultWidgetModel: use default when value is null

Before this change, it was up to individual widget implementations to
actually respect the default value... and most of them didn't.
This change makes respecting the default value automatic!

Author: ctrueden

src/main/java/org/scijava/widget/DefaultWidgetModel.java

@@ -44,6 +44,7 @@
 import org.scijava.module.MethodCallException;
 import org.scijava.module.Module;
 import org.scijava.module.ModuleItem;
+import org.scijava.module.ModuleService;
 import org.scijava.plugin.Parameter;
 import org.scijava.thread.ThreadService;
 import org.scijava.util.ClassUtils;
@@ -70,6 +71,9 @@ public class DefaultWidgetModel extends AbstractContextual implements WidgetMode
 	@Parameter
 	private ConvertService convertService;
 
+	@Parameter
+	private ModuleService moduleService;
+
 	@Parameter(required = false)
 	private LogService log;
 
@@ -84,6 +88,11 @@ public DefaultWidgetModel(final Context context, final InputPanel<?, ?> inputPan
 		this.item = item;
 		this.objectPool = objectPool;
 		convertedObjects = new WeakHashMap<Object, Object>();
+
+		if (item.getValue(module) == null) {
+			// assign the item's default value as the current value
+			setValue(moduleService.getDefaultValue(item));
+		}
 	}
 
 	@Override