def prepare(field, operator, value)
      unless operator =~ /exists|type|size/
        value = value.__expand_complex__
        serializer = serializers[field]
        value = serializer ? serializer.evolve(value) : value
      end
      selection = { operator => value }
      negating? ? { "$not" => selection } : selection
    end
def prepare(field, operator, value)
      unless operator =~ /exists|type|size/
        value = value.__expand_complex__
        serializer = serializers[field]
        value = serializer ? serializer.evolve(value) : value
      end
      selection = { operator => value }
      negating? ? { "$not" => selection } : selection
    end
Prepare the value for merging.

 @api private

 @example Prepare the value.
   mergeable.prepare("field", "$gt", 10)

 @param [ String ] field The name of the field.
 @param [ Object ] value The value.

 @return [ Object ] The serialized value.

 @since 1.0.0