NullPointerException in interceptor

Hi!
I've got a NullPointerException in my interceptor class, but I could find the reason why.

The error log entry:

2005-04-19 14:52:06 StandardWrapperValve[control]: Servlet.service() for servlet control threw exception
java.lang.NullPointerException
    at interceptors.ctoDelete2HistBackInterceptor.preDelete(ctoDelete2HistBackInterceptor.java:32)
    at org.dbforms.event.DbEventInterceptorSupport.preDelete(DbEventInterceptorSupport.java:188)
    at org.dbforms.config.Table.processInterceptors(Table.java:1991)
    at org.dbforms.event.datalist.DeleteEvent.processEvent(DeleteEvent.java:134)
    at org.dbforms.servlets.Controller.process(Controller.java:309)
    at org.dbforms.servlets.Controller.doPost(Controller.java:107)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:763)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
    at org.dbforms.util.external.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:190)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:186)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:214)
    at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
    at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:198)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:152)
    at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:540)
    at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:102)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
    at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
    at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:102)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
    at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:929)
    at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:799)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:705)
    at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:577)
    at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:683)
    at java.lang.Thread.run(Thread.java:534)

The interceptor class:

package interceptors;

import org.dbforms.config.DbFormsConfig;
import org.dbforms.config.FieldValue;
import org.dbforms.config.FieldValues;
import org.dbforms.config.Table;
import org.dbforms.config.ValidationException;

import org.dbforms.event.DbEventInterceptorSupport;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.servlet.http.HttpServletRequest;

public class ctoDelete2HistBackInterceptor extends DbEventInterceptorSupport
{
    public int preDelete(HttpServletRequest request,
            Table              table,
            FieldValues        fieldValues,
            DbFormsConfig      config,
            Connection         con) throws ValidationException
    {
        if (fieldValues != null)
        {
            String strDocID = "";
            String strHistID = "";
            int Row = 0;

            //Here I get my java.lang.NullPointerException:
            strHistID = (String) fieldValues.get("id").getFieldValue();
            strDocID = (String) fieldValues.get("doc_id").getFieldValue();
           
            //Debug:
            //strDocID = "537";
            //strHistID = "1";
            if ((strDocID != null) && (strHistID != ""))
            {
                String backupDocQuery =
                    "INSERT INTO cto_doc_versions (cto_doc_versions.name, cto_doc_versions.doc_id, " +
                    "cto_doc_versions.xdt_file, cto_doc_versions.xdt_file_name, cto_doc_versions.tsl_file, " +
                    "cto_doc_versions.tsl_file_name, cto_doc_versions.last_edit_by, cto_doc_versions.last_edit_time) " +
                    "SELECT cto_docs.name, cto_docs.id, cto_docs.xdt_file, cto_docs.xdt_file_name, cto_docs.tsl_file, " +
                    "cto_docs.tsl_file_name, cto_docs.last_edit_by, cto_docs.last_edit_time " +
                    "FROM cto_docs WHERE cto_docs.id = " + strDocID + ";";
               
                String activateDocQuery =
                    "UPDATE cto_docs, cto_doc_versions SET " +
                    "cto_docs.name = cto_doc_versions.name, cto_docs.xdt_file = cto_doc_versions.xdt_file, " +
                    "cto_docs.xdt_file_name = cto_doc_versions.xdt_file_name, cto_docs.tsl_file = cto_doc_versions.tsl_file, " +
                    "cto_docs.tsl_file_name = cto_doc_versions.tsl_file_name, cto_docs.last_edit_by = cto_doc_versions.last_edit_by, " +
                    "cto_docs.last_edit_time = cto_doc_versions.last_edit_time " +
                    "WHERE cto_doc_versions.id = " + strHistID + " AND cto_doc_versions.doc_id = cto_docs.id;";
                try
                {
                    Statement stmt = con.createStatement();
                    Row = stmt.executeUpdate(backupDocQuery);
                    Row = stmt.executeUpdate(activateDocQuery);               
                    stmt.close();
                }
                catch (SQLException e)
                {
                    System.out.println("Datenbankfehler: "    + e.getMessage());
                    return IGNORE_OPERATION;
                }
            }
        }
        return GRANT_OPERATION;
    }
}

My table definition:

    <table name="cto_doc_versions" defaultVisibleFields="id">
        <field name="id" fieldType="int" size="11" isKey="true" autoInc="true" />
        <field name="name" fieldType="varchar" size="50" />
        <field name="doc_id" fieldType="int" size="11" isKey="true" />
        <field name="xdt_file" fieldType="blob" size="16277215" />
        <field name="xdt_file_name" fieldType="varchar" size="255" />
        <field name="tsl_file" fieldType="blob" size="16277215" />
        <field name="tsl_file_name" fieldType="varchar" size="255" />
        <field name="last_edit_by" fieldType="int" size="11" />
        <field name="last_edit_time" fieldType="timestamp" size="14" />

        <!-- add "granted-privileges" element for security constraints -->
        <interceptor className = "interceptors.ctoDelete2HistBackInterceptor"/>
    </table>

Could anybody give me a hint, where the problem is?

Thanks in advance + regards

Theo