JDBC PostgreSQL

Hello world! J'ai un petit soucis en login sur j2e, j'ai un method qui retourne un objet de type Users, en executant le main, tout va a merveille, mais l'execution en de l'application web, le method doPost de mon servlet releve des exceptions:

java.lang.ClassNotFoundException: org.postgresql.Driver
java.lang.NullPointerException
SELECT * FROM Users WHERE idUsers=1 AND pass=MD5('1234Azerty$')
 at services.dao.General.select(General.java:42)
 at services.models.LoginModel.login(LoginModel.java:15)
 at controllers.Login.doPost(Login.java:56)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:652)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
 at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
 at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
 at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
 at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
 at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
 at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
 at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
 at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1589)
 at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
 at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
 at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
 at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
 at java.base/java.lang.Thread.run(Thread.java:832)
java.lang.NullPointerException
 at services.dao.Connexion.clear(Connexion.java:37)
 at services.models.LoginModel.login(LoginModel.java:22)
 at controllers.Login.doPost(Login.java:56)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:652)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
 at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
 at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
 at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
 at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
 at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
 at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
 at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
 at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1589)
 at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
 at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
 at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
 at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
 at java.base/java.lang.Thread.run(Thread.java:832)