NullPointerException while site:deploy

When attempting site-deploy to sourceforge.net via wagon-ssh, the following NullPointerException is thrown:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-site-plugin:3.0-beta-3:deploy (default-deploy) on project mailhttp: Execution default-deploy of goal org.apache.maven.plugins:maven-site-plugin:3.0-beta-3:deploy failed. NullPointerException -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-site-plugin:3.0-beta-3:deploy (default-deploy) on project mailhttp: Execution default-deploy of goal org.apache.maven.plugins:maven-site-plugin:3.0-beta-3:deploy failed.
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:225)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:59)
at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:319)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:156)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:534)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:196)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:141)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:290)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:230)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:409)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:352)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution default-deploy of goal org.apache.maven.plugins:maven-site-plugin:3.0-beta-3:deploy failed.
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:116)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:209)
... 19 more
Caused by: java.lang.NullPointerException
at org.apache.maven.plugins.site.SiteDeployMojo.configureWagon(SiteDeployMojo.java:474)
at org.apache.maven.plugins.site.SiteDeployMojo.execute(SiteDeployMojo.java:216)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:107)
... 20 more