Value for mesos attributes is not optional

Mesos documentation describes attributes as following

Attributes are key-value pairs (where value is optional) ...

There is no way to start an agent with attribute w/o value, i. e. with key set only.

Neither with

--attributes=bla

nor

--attributes=bla:

You'll get the following errors

attributes.cpp:145] Invalid attribute key:value pair 'bla'

or

attributes.cpp:145] Invalid attribute key:value pair 'bla:'

accordingly

Agent code should allow setting attributes without value according to documentation. This should be fixed in both mesos-agent binary and mesos-init-wrapper script

If documentation is wrong the web page describing roles has to be fixed.