def to_h
      {
        id:             id,
        uuid:           uuid,
        aggregate_id:   aggregate_id,
        type:           type,
        body:           body,
        version:        version,
        created_at:     created_at,
        correlation_id: correlation_id,
        causation_id:   causation_id,
      }
    end
def to_h
      {
        id:             id,
        uuid:           uuid,
        aggregate_id:   aggregate_id,
        type:           type,
        body:           body,
        version:        version,
        created_at:     created_at,
        correlation_id: correlation_id,
        causation_id:   causation_id,
      }
    end
returns a hash of the event attributes

 @return Hash