class Exception

def as_json(*)


Exception.json_create(x) # => #

\Method +JSON.create+ deserializes such a hash, returning a \Exception object:

x = Exception.new('Foo').as_json # => {"json_class"=>"Exception", "m"=>"Foo", "b"=>nil}
require 'json/add/exception'

returning a 2-element hash representing +self+:
\Method Exception#as_json serializes +self+,

see Marshal[https://docs.ruby-lang.org/en/master/Marshal.html].
to serialize and deserialize a \Exception object;
Methods Exception#as_json and +Exception.json_create+ may be used 
def as_json(*)
  {
    JSON.create_id => self.class.name,
    'm'            => message,
    'b'            => backtrace,
  }
end