Tried to save a GMK file as a GMX and got a big error

[GithubGuy420]

LateralGM Version: 1.8.234
Working Directory: C:\ENIGMA\enigma-dev\lateralgm.jar

Operating System: Windows 10
Version: 10.0
Architecture: amd64

Java Name: Java HotSpot(TM) 64-Bit Server VM
Java Vendor: Oracle Corporation
Version: 16.0.1

Current Thread: AWT-EventQueue-0
Available processors (cores): 8
Free memory (bytes): 96430224
Maximum memory (bytes): 4091543552
Total memory available to JVM (bytes): 585105408

File system root: C:
Total space (bytes): 510745636864
Free space (bytes): 360374616064
Usable space (bytes): 360374616064

Stack trace:
java.util.concurrent.ExecutionException: org.lateralgm.file.GmFormatException: javax.imageio.IIOException: Can't create an ImageOutputStream!
at java.base/java.util.concurrent.FutureTask.report(Unknown Source)
at java.base/java.util.concurrent.FutureTask.get(Unknown Source)
at java.desktop/javax.swing.SwingWorker.get(Unknown Source)
at org.lateralgm.main.FileChooser.save(FileChooser.java:910)
at org.lateralgm.main.FileChooser.saveNewFile(FileChooser.java:838)
at org.lateralgm.main.Listener.actionPerformed(Listener.java:563)
at java.desktop/javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at java.desktop/javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at java.desktop/javax.swing.AbstractButton.doClick(Unknown Source)
at java.desktop/javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
at java.desktop/javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
at java.desktop/java.awt.Component.processMouseEvent(Unknown Source)
at java.desktop/javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.desktop/java.awt.Component.processEvent(Unknown Source)
at java.desktop/java.awt.Container.processEvent(Unknown Source)
at java.desktop/java.awt.Component.dispatchEventImpl(Unknown Source)
at java.desktop/java.awt.Container.dispatchEventImpl(Unknown Source)
at java.desktop/java.awt.Component.dispatchEvent(Unknown Source)
at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.desktop/java.awt.Container.dispatchEventImpl(Unknown Source)
at java.desktop/java.awt.Window.dispatchEventImpl(Unknown Source)
at java.desktop/java.awt.Component.dispatchEvent(Unknown Source)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.desktop/java.awt.EventQueue$4.run(Unknown Source)
at java.desktop/java.awt.EventQueue$4.run(Unknown Source)
at java.base/java.security.AccessController.doPrivileged(Unknown Source)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.desktop/java.awt.EventQueue$5.run(Unknown Source)
at java.desktop/java.awt.EventQueue$5.run(Unknown Source)
at java.base/java.security.AccessController.doPrivileged(Unknown Source)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.desktop/java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.desktop/java.awt.EventDispatchThread.run(Unknown Source)
Caused by: org.lateralgm.file.GmFormatException: javax.imageio.IIOException: Can't create an ImageOutputStream!
at java.desktop/javax.imageio.ImageIO.write(Unknown Source)
at org.lateralgm.file.GMXFileWriter.writeSprite(GMXFileWriter.java:640)
at org.lateralgm.file.GMXFileWriter.writeTree(GMXFileWriter.java:378)
at org.lateralgm.file.GMXFileWriter.writeGroup(GMXFileWriter.java:346)
at org.lateralgm.file.GMXFileWriter.writeProjectFile(GMXFileWriter.java:214)
at org.lateralgm.main.FileChooser$GMXIO.write(FileChooser.java:585)
at org.lateralgm.main.FileChooser.save(FileChooser.java:951)
at org.lateralgm.main.FileChooser$3.doInBackground(FileChooser.java:893)
at java.desktop/javax.swing.SwingWorker$1.call(Unknown Source)
at java.base/java.util.concurrent.FutureTask.run(Unknown Source)
at java.desktop/javax.swing.SwingWorker.run(Unknown Source)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.base/java.lang.Thread.run(Unknown Source)

how do i fix this?