MojoException while running update or create

[hakan42]

If project fails to be updates, values in ProjectJsonResponse can become null, leading to an NullPointerException in Hashtable.put:

[ERROR] Failed to execute goal com.versioneye:versioneye-maven-plugin:2.1.0-SNAPSHOT:update (default-cli) on project xing-sync: Oh no! Something went wrong. Get in touch with the VersionEye guys and give them feedback.You find them on Twitter at https//twitter.com/VersionEye. NullPointerException -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal com.versioneye:versioneye-maven-plugin:2.1.0-SNAPSHOT:update (default-cli) on project xing-sync: Oh no! Something went wrong. Get in touch with the VersionEye guys and give them feedback.You find them on Twitter at https//twitter.com/VersionEye.
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:217)
...
...
...
        at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:352)
Caused by: org.apache.maven.plugin.MojoExecutionException: Oh no! Something went wrong. Get in touch with the VersionEye guys and give them feedback.You find them on Twitter at https//twitter.com/VersionEye.
        at com.versioneye.UpdateMojo.execute(UpdateMojo.java:32)
        at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:101)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:209)
        ... 19 more
Caused by: java.lang.NullPointerException
        at java.util.Hashtable.put(Hashtable.java:514)
        at java.util.Properties.setProperty(Properties.java:161)
        at com.versioneye.SuperMojo.writeProperties(SuperMojo.java:141)
        at com.versioneye.UpdateMojo.execute(UpdateMojo.java:29)
        ... 21 more

Therefore, guard against null values in ProjectJsonResponse