While I click save for saving the Editable Email Notification after customizing the trigger for always , the below is message is get. It does not allow me to save.

A problem occurred while processing the request. Please check our bug tracker to see if a similar problem has already been reported. If it is already reported, please vote and put a comment on it to let us gauge the impact of the problem. If you think this is a new issue, please file a new issue. When you file an issue, make sure to add the entire stack trace, along with the version of Jenkins and relevant plugins. The users list might be also useful in understanding what has happened.
Stack trace

javax.servlet.ServletException: java.lang.RuntimeException: Failed to instantiate class hudson.plugins.emailext.ExtendedEmailPublisher from {"project_disabled":false,"project_recipient_list":"$DEFAULT_RECIPIENTS","project_replyto":"$DEFAULT_REPLYTO","project_content_type":"default","project_default_subject":"$DEFAULT_SUBJECT","project_default_content":"$DEFAULT_CONTENT","project_attachments":"","project_attach_buildlog":"0","project_presend_script":"$DEFAULT_PRESEND_SCRIPT","project_save_output":false,"project_triggers":[

{"stapler-class":"","$class":""}

,

{"stapler-class":"","$class":""}

,

{"stapler-class":"","$class":""}

,

{"stapler-class":"","$class":""}

,{"recipientProviders":[

{"stapler-class":"hudson.plugins.emailext.plugins.recipients.DevelopersRecipientProvider","$class":"hudson.plugins.emailext.plugins.recipients.DevelopersRecipientProvider"}

,

{"stapler-class":"hudson.plugins.emailext.plugins.recipients.ListRecipientProvider","$class":"hudson.plugins.emailext.plugins.recipients.ListRecipientProvider"}

],"recipientList":"chauhanheena@gmail.com","replyTo":"$PROJECT_DEFAULT_REPLYTO","contentType":"both","subject":"$PROJECT_DEFAULT_SUBJECT","body":"$PROJECT_DEFAULT_CONTENT","attachmentsPattern":"","attachBuildLog":"0","stapler-class":"hudson.plugins.emailext.plugins.trigger.AlwaysTrigger","$class":"hudson.plugins.emailext.plugins.trigger.AlwaysTrigger"}],"stapler-class":"hudson.plugins.emailext.ExtendedEmailPublisher","$class":"hudson.plugins.emailext.ExtendedEmailPublisher"}
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:796)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
at org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:249)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:649)
at org.kohsuke.stapler.Stapler.service(Stapler.java:238)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:686)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1494)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:123)
at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:114)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:48)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:171)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:49)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:81)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:30)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1474)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:499)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137)
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:533)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1086)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:428)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1020)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
at org.eclipse.jetty.server.Server.handle(Server.java:370)
at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:489)
at org.eclipse.jetty.server.AbstractHttpConnection.content(AbstractHttpConnection.java:960)
at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.content(AbstractHttpConnection.java:1021)
at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:865)
at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:240)
at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:668)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:52)
at winstone.BoundedExecutorService$1.run(BoundedExecutorService.java:77)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.RuntimeException: Failed to instantiate class hudson.plugins.emailext.ExtendedEmailPublisher from {"project_disabled":false,"project_recipient_list":"$DEFAULT_RECIPIENTS","project_replyto":"$DEFAULT_REPLYTO","project_content_type":"default","project_default_subject":"$DEFAULT_SUBJECT","project_default_content":"$DEFAULT_CONTENT","project_attachments":"","project_attach_buildlog":"0","project_presend_script":"$DEFAULT_PRESEND_SCRIPT","project_save_output":false,"project_triggers":[

{"stapler-class":"","$class":""}

,

{"stapler-class":"","$class":""}

,

{"stapler-class":"","$class":""}

,

{"stapler-class":"","$class":""}

,{"recipientProviders":[

{"stapler-class":"hudson.plugins.emailext.plugins.recipients.DevelopersRecipientProvider","$class":"hudson.plugins.emailext.plugins.recipients.DevelopersRecipientProvider"}

,

{"stapler-class":"hudson.plugins.emailext.plugins.recipients.ListRecipientProvider","$class":"hudson.plugins.emailext.plugins.recipients.ListRecipientProvider"}

],"recipientList":"chauhanheena@gmail.com","replyTo":"$PROJECT_DEFAULT_REPLYTO","contentType":"both","subject":"$PROJECT_DEFAULT_SUBJECT","body":"$PROJECT_DEFAULT_CONTENT","attachmentsPattern":"","attachBuildLog":"0","stapler-class":"hudson.plugins.emailext.plugins.trigger.AlwaysTrigger","$class":"hudson.plugins.emailext.plugins.trigger.AlwaysTrigger"}],"stapler-class":"hudson.plugins.emailext.ExtendedEmailPublisher","$class":"hudson.plugins.emailext.ExtendedEmailPublisher"}
at hudson.model.Descriptor.newInstance(Descriptor.java:579)
at hudson.model.Descriptor.newInstancesFromHeteroList(Descriptor.java:941)
at hudson.model.Descriptor.newInstancesFromHeteroList(Descriptor.java:903)
at hudson.util.DescribableList.rebuildHetero(DescribableList.java:208)
at hudson.model.Project.submit(Project.java:236)
at hudson.model.Job.doConfigSubmit(Job.java:1206)
at hudson.model.AbstractProject.doConfigSubmit(AbstractProject.java:788)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:298)
at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:161)
at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:96)
at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:121)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
... 48 more
Caused by: java.lang.IllegalArgumentException: Failed to instantiate class hudson.plugins.emailext.ExtendedEmailPublisher from {"project_disabled":false,"project_recipient_list":"$DEFAULT_RECIPIENTS","project_replyto":"$DEFAULT_REPLYTO","project_content_type":"default","project_default_subject":"$DEFAULT_SUBJECT","project_default_content":"$DEFAULT_CONTENT","project_attachments":"","project_attach_buildlog":"0","project_presend_script":"$DEFAULT_PRESEND_SCRIPT","project_save_output":false,"project_triggers":[

{"stapler-class":"","$class":""}

,

{"stapler-class":"","$class":""}

,

{"stapler-class":"","$class":""}

,

{"stapler-class":"","$class":""}

,{"recipientProviders":[

{"stapler-class":"hudson.plugins.emailext.plugins.recipients.DevelopersRecipientProvider","$class":"hudson.plugins.emailext.plugins.recipients.DevelopersRecipientProvider"}

,

{"stapler-class":"hudson.plugins.emailext.plugins.recipients.ListRecipientProvider","$class":"hudson.plugins.emailext.plugins.recipients.ListRecipientProvider"}

],"recipientList":"chauhanheena@gmail.com","replyTo":"$PROJECT_DEFAULT_REPLYTO","contentType":"both","subject":"$PROJECT_DEFAULT_SUBJECT","body":"$PROJECT_DEFAULT_CONTENT","attachmentsPattern":"","attachBuildLog":"0","stapler-class":"hudson.plugins.emailext.plugins.trigger.AlwaysTrigger","$class":"hudson.plugins.emailext.plugins.trigger.AlwaysTrigger"}],"stapler-class":"hudson.plugins.emailext.ExtendedEmailPublisher","$class":"hudson.plugins.emailext.ExtendedEmailPublisher"}
at org.kohsuke.stapler.RequestImpl$TypePair.convertJSON(RequestImpl.java:602)
at org.kohsuke.stapler.RequestImpl.bindJSON(RequestImpl.java:404)
at org.kohsuke.stapler.RequestImpl.bindJSON(RequestImpl.java:400)
at hudson.model.Descriptor.newInstance(Descriptor.java:570)
... 64 more
Caused by: java.lang.IllegalArgumentException: Failed to convert the project_triggers parameter of the constructor public hudson.plugins.emailext.ExtendedEmailPublisher(java.lang.String,java.lang.String,java.lang.String,java.lang.String,java.lang.String,java.lang.String,int,java.lang.String,boolean,java.util.List,hudson.plugins.emailext.MatrixTriggerMode,boolean,java.util.List)
at org.kohsuke.stapler.RequestImpl.instantiate(RequestImpl.java:699)
at org.kohsuke.stapler.RequestImpl.access$200(RequestImpl.java:81)
at org.kohsuke.stapler.RequestImpl$TypePair.convertJSON(RequestImpl.java:600)
... 67 more
Caused by: java.lang.IllegalArgumentException: Failed to instantiate class hudson.plugins.emailext.plugins.EmailTrigger from

{"stapler-class":"","$class":""}

at org.kohsuke.stapler.RequestImpl$TypePair.convertJSON(RequestImpl.java:602)
at org.kohsuke.stapler.RequestImpl$TypePair.convertJSON(RequestImpl.java:647)
at org.kohsuke.stapler.RequestImpl.bindJSON(RequestImpl.java:404)
at org.kohsuke.stapler.RequestImpl.instantiate(RequestImpl.java:697)
... 69 more
Caused by: java.lang.IllegalArgumentException: Class is specified in JSON, but no such class found in classLoader hudson.PluginManager$UberClassLoader
at org.kohsuke.stapler.RequestImpl$TypePair.convertJSON(RequestImpl.java:596)
... 72 more
Caused by: java.lang.ClassNotFoundException: cached miss for
at hudson.PluginManager$UberClassLoader.findClass(PluginManager.java:1105)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at org.kohsuke.stapler.RequestImpl$TypePair.convertJSON(RequestImpl.java:591)
... 72 more