com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry 'null' for key 1

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)

at java.lang.reflect.Constructor.newInstance(Constructor.java:513)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)

at com.mysql.jdbc.Util.getInstance(Util.java:386)

at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1039)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3597)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3529)

at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1990)

at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2151)

at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2619)

at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1709)

at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1628)

at test.DBBean.update(DBBean.java:44)

at org.apache.jsp.mainpage_jsp._jspService(mainpage_jsp.java:116)

at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)

at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)

at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:261)

at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)

at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:581)

at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)

at java.lang.Thread.run(Thread.java:662)