Strange Error Writing XML encoded file

[raven lynx]

I'm saving / restoring GUI program state using an XML file. SplitPane divider and table column widths. Something is wrong with loading up the class to encode. But error is very obscure. Here is a chunk of code and the error.

[brazen root]

<@&987246487241105418> please have a look, thanks.

[raven lynx]

Here's the class and the save / restore code. The picture shows the error during a debug session.

[brazen root]

@raven lynx

Your question has been closed due to inactivity.

If it was not resolved yet, feel free to just post a message below
to reopen it, or create a new thread.

Note that usually the reason for nobody calling back is that your
question may have been not well asked and hence no one felt confident
enough answering.

When you reopen the thread, try to use your time to improve the quality
of the question by elaborating, providing details, context, all relevant code
snippets, any errors you are getting, concrete examples and perhaps also some
screenshots. Share your attempt, explain the expected results and compare
them to the current results.

Also try to make the information easily accessible by sharing code
or assignment descriptions directly on Discord, not behind a link or
PDF-file; provide some guidance for long code snippets and ensure
the code is well formatted and has syntax highlighting. Kindly read through
https://stackoverflow.com/help/how-to-ask for more.

With enough info, someone knows the answer for sure 👍

[raven lynx]

/*
Class to hold GUI stuff to save / restore in an XML file
*/
public class SyncFilesGuiStuffToSave {

public SimpleDoubleProperty dSplitDivider;
public SimpleDoubleProperty dPairTableNameWidth;
public SimpleDoubleProperty dPairTableStatusWidth;
public SimpleDoubleProperty dTreeTableWidth0;
public SimpleDoubleProperty dTreeTableWidth1;
public SimpleDoubleProperty dTreeTableWidth2;
public SimpleDoubleProperty dTreeTableWidth3;


public SyncFilesGuiStuffToSave() {

}

public double getDSplitDivider() { return dSplitDivider.get(); }
public double getDPairTableNameWidth() { return dPairTableNameWidth.get(); }
public double getDPairTableStatusWidth() { return dPairTableStatusWidth.get(); }
public double getDTreeTableWidth0() { return dTreeTableWidth0.get(); }
public double getDTreeTableWidth1() { return dTreeTableWidth1.get(); }
public double getDTreeTableWidth2() { return dTreeTableWidth2.get(); }
public double getDTreeTableWidth3() { return dTreeTableWidth3.get(); }

public void setDSplitDivider( double div ) { this.dSplitDivider = new SimpleDoubleProperty( div ); }
public void setDPairTableNameWidth( double div ) { this.dPairTableNameWidth = new SimpleDoubleProperty( div ); }
public void setDPairTableStatusWidth( double div ) { this.dPairTableStatusWidth = new SimpleDoubleProperty( div ); }
public void setDTreeTableWidth0( double div ) { this.dTreeTableWidth0 = new SimpleDoubleProperty( div ); }
public void setDTreeTableWidth1( double div ) { this.dTreeTableWidth1 = new SimpleDoubleProperty( div ); }
public void setDTreeTableWidth2( double div ) { this.dTreeTableWidth2 = new SimpleDoubleProperty( div ); }
public void setDTreeTableWidth3( double div ) { this.dTreeTableWidth3 = new SimpleDoubleProperty( div ); }

}

Class needs to look like this to work with encode/decode