java null pointer exception when loading a resource

Hi,

the attached code fails on the line
'builder.addPackageFromDrl(new InputStreamReader( Rule_Loader.class.getResourceAsStream( listOfFiles[i].toString() ) ) ); '

with a null pointer exception thrown.

the file exists and is' C:\myworkspace\settlement_engine\rules\TENNIS\2001.drl'

Can anybody see whatim doing wrong?

thanks in advance
Alex

import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
 
import org.drools.RuleBase;
import org.drools.RuleBaseFactory;
import org.drools.compiler.DroolsParserException;
import org.drools.compiler.PackageBuilder;
import org.drools.rule.Package;
 
import com.paddypower.ramp.settlement_engine.misc.Constants;
 
/**
 * loads all rules for the specified sport type
 * 
 * @author 
 *
 */
public class Rule_Loader {
 
	public RuleBase load_rules(String sport_type){
		RuleBase rulebase = null;
		
		try{
			RuleBase ruleBase = RuleBaseFactory.newRuleBase();
		    PackageBuilder builder = new PackageBuilder();
			File folder = new File(Constants.RULES_FILE + "/" + sport_type);
			File[] listOfFiles = folder.listFiles();
			 for (int i = 0; i < listOfFiles.length; i++) {
			      if (listOfFiles[i].isFile()) 
			    	  builder.addPackageFromDrl(new InputStreamReader( Rule_Loader.class.getResourceAsStream( listOfFiles[i].toString() ) ) ); 
			}
			Package pkg = builder.getPackage();
		    ruleBase.addPackage( pkg );
			return rulebase;
		}
		catch(IOException ioe){System.out.println(ioe.toString());return rulebase = null;}
		catch(DroolsParserException dpe){System.out.println(dpe.toString());return rulebase = null;}
		catch(Exception e){System.out.println(e.toString());
			return rulebase = null;}
	}
	
	
}

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