Java Nul error despite scripts working and data extracted

I have a simple scrape session pulling two peices of datae from 1 table row. The extractor patterns are working correctly (when I apply pattern to last scraped data it displays correctly for both extractor patterns). I have also edited each token multiple times to verify "save in session variable' is checked for both.

I am running my Write_Data_To_File script after each pattern is applied.

No matter what I check the log always shows:

java.lang.NullPointerException BSF info:null at line: 0 column: columnNo

Please suggest what may be causing this?

The Interpreted Java code for my Write_Data_To_File script is:

// Output a message to the log so we know that we'll be writing the text out to a file.
session.log( "Writing data to a file." );

// Create a FileWriter object that we'll use to write out the text.
out = new FileWriter( "data.txt", true );

// Remove &amp signs from artist name
artistName = session.getVariable( "artist_name" );
artistName = artistName.replaceAll( "&", "&" );
session.setVariable( "artist_name", artistName );

// Remove &amp signs from track name
trackName = session.getVariable( "track_name" );
trackName = trackName.replaceAll( "&", "&" );
session.setVariable( "track_name", trackName );

// Write out the text.
//Write out the individual scraped elements------------------------------
out.write( session.getVariable( "track_name" )+ "\t");
out.write( session.getVariable( "artist_name"+ "\t"));
//Insert the line break to seperate records------------------------------
out.write("\r");

// Close the file.-------------------------------------------------------
out.close();