LPS-37741 Changed condition check to match the way com.liferay.portlet.assetpublisher.action.ConfigurationActionImpl.updateDisplaySettings(ActionRequest) stores preferences
LPS-37741 Make sure all assets can be added when displayStyle is manual
LPS-37741 Removed unused annotation
LPS-37741 Added tests to show inconsistent behaviour
LPS-37741 Added missing validation methods for arrays of primitives

Before this, one could think that calling Validator.isNull(new int[]{}) was behaving like Validator.isNull(new Object[]{}) but it was really invoking Validator.isNull(Object obj)
LPS-37741 Changed condition checking to use new Validator methods
LPS-37741 Alex Chow added the isNull(for arrays), but I've generally avoided using them, and just stick to using them for Strings. If I could go back, I would have never added those additional methods, and may deprecate the other non String isNull for the future.