SwingObjectWidget: guard versus empty choices list

The choices list might be non-null but empty. We guard against this in
various other places, but the test here was missing. So let's add it.
Hopefully this addresses the bug of empty choice dropdowns!

Author: ctrueden

src/main/java/org/scijava/ui/swing/widget/SwingObjectWidget.java

@@ -78,10 +78,11 @@ public Object getValue() {
 	public void set(final WidgetModel model) {
 		super.set(model);
 
-		String[] availableChoices = model.getChoices();
-		if (availableChoices != null) {
-			comboBox = new JComboBox<>(availableChoices);
-		} else {
+		String[] choices = model.getChoices();
+		if (choices != null && choices.length > 0) {
+			comboBox = new JComboBox<>(choices);
+		}
+		else {
 			comboBox = new JComboBox<>(model.getObjectPool().toArray());
 		}
 		setToolTip(comboBox);
@@ -96,8 +97,10 @@ public void set(final WidgetModel model) {
 
 	@Override
 	public boolean supports(final WidgetModel model) {
-		return super.supports(model) && ((model.getChoices() != null && model.getChoices().length>0) ||
-			((model.getObjectPool() != null) && (model.getObjectPool().size() > 0)));
+		return super.supports(model) && (
+			(model.getChoices() != null && model.getChoices().length > 0) ||
+			(model.getObjectPool() != null && model.getObjectPool().size() > 0)
+		);
 	}
 
 	// -- AbstractUIInputWidget methods ---