NPE when plugin is not configured

Caused by: java.lang.NullPointerException
        at javax.mail.internet.InternetAddress.parse(InternetAddress.java:609)
        at javax.mail.internet.InternetAddress.parse(InternetAddress.java:569)
        at javax.mail.internet.InternetAddress.<init>(InternetAddress.java:105)
        at org.apache.commons.mail.Email.createInternetAddress(Email.java:578)
        at org.apache.commons.mail.Email.setFrom(Email.java:668)
        at org.apache.commons.mail.Email.setFrom(Email.java:651)
        at org.apache.commons.mail.Email.setFrom(Email.java:631)
        at org.sonar.plugins.email.EmailPublisher.executeOn(EmailPublisher.java:80)
        at org.sonar.batch.phases.PostJobsExecutor.execute(PostJobsExecutor.java:58)
        at org.sonar.batch.phases.Phases.execute(Phases.java:82)
        at org.sonar.batch.ProjectBatch.execute(ProjectBatch.java:55)
        at org.sonar.batch.Batch.analyzeModule(Batch.java:161)
        at org.sonar.batch.Batch.analyzeModules(Batch.java:106)
        at org.sonar.batch.Batch.execute(Batch.java:66)
        at org.sonar.maven3.SonarMojo.executeBatch(SonarMojo.java:144)
        at org.sonar.maven3.SonarMojo.execute(SonarMojo.java:135)
        at org.codehaus.mojo.sonar.Bootstraper.executeMojo(Bootstraper.java:113)
        ... 23 more