Chef12 undefined method validate_spec, how to fix?

Question

Chef

Good afternoon!
We are currently moving to chef12 from chef11. There was a problem with one of the cookbooks.
cookbook syslog_ng.
There is a line in the resources:
attribute :host, :kind_of => String, :default => '', :callbacks => { 'should not be empty' => lambda { |spec| validate_spec(spec) } }
It is not accepted by the 12 boss, and it throws an error:

/var/chef/cache/cookbooks/cron/resources/d.rb:65: warning: constant ::Fixnum is deprecated

================================================================================
Recipe Compile Error in /var/chef/cache/cookbooks/syslog_ng/resources/destination_syslog.rb
================================================================================

NoMethodError
-------------
undefined method `validate_spec' for #<Class:0x00000000052607c8>

Cookbook Trace:
  /var/chef/cache/cookbooks/syslog_ng/resources/destination_syslog.rb:11:in `block in class_from_file'
  /var/chef/cache/cookbooks/syslog_ng/resources/destination_syslog.rb:11:in `class_from_file'

I ask for help, how can I remake it under 12 chief? Thanks a lot.
ps tried changing it to
attribute :host, :kind_of => String, :default => '', :callbacks => { 'should not be empty' => lambda { |spec| validate_spec(spec) } }
the cookbook started, but the syslog didn't start at all after it was applied