Opening a folder in the "Playlist Directory" throws an Exception

[Borewit]

Reproduced this issue in versions: 2.4.0, v2.5.1

java.lang.NullPointerException: Cannot invoke "java.util.Collection.toArray()" because "c" is null
	at java.util.ArrayList.addAll(ArrayList.java:670) ~[?:?]
	at listfix.util.FileTypeSearch.findFiles(FileTypeSearch.java:62) ~[main/:?]
	at listfix.view.GUIScreen.lambda$openTreeSelectedPlaylists$34(GUIScreen.java:1288) ~[main/:?]
	at java.util.ArrayList.forEach(ArrayList.java:1511) ~[?:?]
	at listfix.view.GUIScreen.openTreeSelectedPlaylists(GUIScreen.java:1285) ~[main/:?]
	at listfix.view.GUIScreen._btnOpenSelectedActionPerformed(GUIScreen.java:2570) ~[main/:?]
	at listfix.view.GUIScreen.lambda$initComponents$10(GUIScreen.java:905) ~[main/:?]
	at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1967) ~[?:?]
	at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2308) ~[?:?]
	at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405) ~[?:?]
	at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262) ~[?:?]
	at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:279) ~[?:?]
	at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:298) ~[?:?]
	at java.awt.Component.processMouseEvent(Component.java:6614) ~[?:?]
	at javax.swing.JComponent.processMouseEvent(JComponent.java:3342) ~[?:?]
	at java.awt.Component.processEvent(Component.java:6379) ~[?:?]
	at java.awt.Container.processEvent(Container.java:2263) ~[?:?]
	at java.awt.Component.dispatchEventImpl(Component.java:4990) ~[?:?]
	at java.awt.Container.dispatchEventImpl(Container.java:2321) ~[?:?]
	at java.awt.Component.dispatchEvent(Component.java:4822) ~[?:?]
	at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4919) ~[?:?]
	at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4548) ~[?:?]
	at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4489) ~[?:?]
	at java.awt.Container.dispatchEventImpl(Container.java:2307) ~[?:?]
	at java.awt.Window.dispatchEventImpl(Window.java:2769) ~[?:?]
	at java.awt.Component.dispatchEvent(Component.java:4822) ~[?:?]
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:772) ~[?:?]
	at java.awt.EventQueue$4.run(EventQueue.java:721) ~[?:?]
	at java.awt.EventQueue$4.run(EventQueue.java:715) ~[?:?]
	at java.security.AccessController.doPrivileged(AccessController.java:391) ~[?:?]
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85) ~[?:?]
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:95) ~[?:?]
	at java.awt.EventQueue$5.run(EventQueue.java:745) ~[?:?]
	at java.awt.EventQueue$5.run(EventQueue.java:743) ~[?:?]
	at java.security.AccessController.doPrivileged(AccessController.java:391) ~[?:?]
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85) ~[?:?]
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:742) ~[?:?]
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203) ~[?:?]
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124) ~[?:?]
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113) ~[?:?]
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109) ~[?:?]
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101) ~[?:?]
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:90) ~[?:?]