Server startup error when using collector_expiration_threshold config option

[bernd]

Source: https://groups.google.com/forum/?hl=en#!topic/graylog2/KLHsZ-0SUFI

When starting graylog with the following function enabled it fails on bootup.

collector_expiration_threshold = 14d (or 20d or 30d)

Fail message:

Exception in thread "main" java.lang.ClassCastException: com.github.joschi.jadconfig.util.Duration cannot be cast to java.lang.Integer
        at com.github.joschi.jadconfig.validators.PositiveIntegerValidator.validate(PositiveIntegerValidator.java:11)
        at com.github.joschi.jadconfig.JadConfig.validateParameter(JadConfig.java:207)
        at com.github.joschi.jadconfig.JadConfig.processClassFields(JadConfig.java:141)
        at com.github.joschi.jadconfig.JadConfig.process(JadConfig.java:99)
        at org.graylog2.bootstrap.CmdLineTool.readConfiguration(CmdLineTool.java:316)
        at org.graylog2.bootstrap.CmdLineTool.run(CmdLineTool.java:161)
        at org.graylog2.bootstrap.Main.main(Main.java:58)

Centos 6.6 and either with java 1.7 or 1.8