Gerando PDF

ExceptionConverter : java.lang.nullPointerException

public void createPDF(String as_pdf){
        try{
            JasperExportManager.exportReportToPdfFile(createReport(),"historico.pdf");
        }catch(JRException exc){
            System.out.println("Report.createPDF : " + exc);
        }
    }
public JasperPrint createReport(){
        try{
            /**Carregando arquivo xml*/
            java.io.File file=new java.io.File(gs_xml);
            if(!file.exists()){
                javax.swing.JOptionPane.showMessageDialog(null,"Arquivo não encontrado
" + gs_xml);
                return null;
            }else{
                JasperDesign jasperDesign = JasperManager.loadXmlDesign(file.getPath());
                JasperReport jasperReport = JasperManager.compileReport(jasperDesign);
                
                // Setando os dados do relatorio
                JasperPrint jasperPrint = JasperManager.fillReport(jasperReport, map_param, objetos.ConexaoOracleEstatica.getConexao());
                return jasperPrint;
            }
        }catch(Exception exc){
            System.out.println("Report.createReport : " + exc);
            return null;
        }
    }