Build failure due to email notification issue

ERROR: Build step failed with exception
org.springframework.security.authentication.DisabledException: The user "null" is administratively disabled.
	at hudson.security.UserAttributesHelper.checkIfUserEnabled(UserAttributesHelper.java:92)
	at hudson.security.LDAPSecurityRealm$LDAPUserDetailsService.loadUserByUsername(LDAPSecurityRealm.java:1314)
	at hudson.security.LDAPSecurityRealm$DelegateLDAPUserDetailsService.loadUserByUsername(LDAPSecurityRealm.java:1227)
	at jenkins.security.ImpersonatingUserDetailsService2.loadUserByUsername(ImpersonatingUserDetailsService2.java:29)
	at hudson.model.User.getUserDetailsForImpersonation2(User.java:399)
	at hudson.model.User.impersonate2(User.java:367)
	at hudson.model.User.impersonate(User.java:377)
Caused: org.acegisecurity.DisabledException: org.springframework.security.authentication.DisabledException: The user "null" is administratively disabled.; nested exception is org.springframework.security.authentication.DisabledException: The user "null" is administratively disabled.
	at org.acegisecurity.DisabledException.fromSpring(DisabledException.java:51)
	at org.acegisecurity.AuthenticationException.fromSpring(AuthenticationException.java:88)
	at hudson.model.User.impersonate(User.java:379)
	at hudson.tasks.MailSender.getUserEmailList(MailSender.java:471)
	at hudson.tasks.MailSender.createEmptyMail(MailSender.java:394)
	at hudson.tasks.MailSender.createBackToNormalMail(MailSender.java:211)
	at hudson.tasks.MailSender.createMail(MailSender.java:196)
	at hudson.tasks.MailSender.run(MailSender.java:111)
	at hudson.tasks.Mailer.perform(Mailer.java:176)
	at hudson.tasks.Mailer.perform(Mailer.java:139)
	at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
	at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:803)
	at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:752)
	at hudson.model.Build$BuildExecution.post2(Build.java:177)
	at hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:697)
	at hudson.model.Run.execute(Run.java:1932)
	at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
	at hudson.model.ResourceController.execute(ResourceController.java:97)
	at hudson.model.Executor.run(Executor.java:429)
Build step 'E-mail Notification' marked build as failure
Finished: FAILURE