To prevent a number of duplicate bugs and potential for loss of a configured value in an option, as of this post, we have applied a hot fix to the beta 2 package to prevent this issue. Any downloads after the date of this post will include this fix.
If you receive this error and wish to workaround it, please find the following in src/XF/Entity/Option.php:
'option_value' => true,
And add this code after it:
'optionValue' => false,
Note that this is a temporary workaround, specific to beta 2. Developers should not rely on the "optionValue" getter.