throw an error when type is unsupported

lib/config/locales/en.yml

@@ -27,4 +27,7 @@ en:
             message: "Unsupported field type."
             summary: "The type of the field '%{field}' is not supported: %{type}."
             resolution: "Please open a feature request in https://github.com/mongoid/mongoid-scroll."
-
+          unsupported_type:
+            message: "Unsupported type."
+            summary: "The type supplied in the cursor is not supported: %{type}."
+            resolution: "The cursor type can be either ':previous' or ':next'."

lib/mongoid/scroll/base_cursor.rb

@@ -11,6 +11,8 @@ def initialize(value, options = {})
         @direction = options[:direction] || 1
         @include_current = options[:include_current] || false
         @type = options[:type] || :next
+
+        raise Mongoid::Scroll::Errors::UnsupportedTypeError.new(type: @type) if ![:previous, :next].include?(@type)
       end
 
       def criteria

lib/mongoid/scroll/errors.rb

@@ -6,3 +6,4 @@
 require 'mongoid/scroll/errors/invalid_base64_cursor_error'
 require 'mongoid/scroll/errors/no_such_field_error'
 require 'mongoid/scroll/errors/unsupported_field_type_error'
+require 'mongoid/scroll/errors/unsupported_type_error'

lib/mongoid/scroll/errors/unsupported_type_error.rb

@@ -0,0 +1,11 @@
+module Mongoid
+  module Scroll
+    module Errors
+      class UnsupportedTypeError < Mongoid::Scroll::Errors::Base
+        def initialize(opts = {})
+          super(compose_message('unsupported_type', opts))
+        end
+      end
+    end
+  end
+end

spec/mongoid/cursor_spec.rb

@@ -131,6 +131,14 @@
       end.to raise_error ArgumentError
     end
   end
+  context 'an invalid type cursor' do
+    let(:feed_item) { Feed::Item.create!(a_string: 'astring') }
+    it 'raises Mongoid::Scroll::Errors::UnsupportedTypeError' do
+      expect do
+        Mongoid::Scroll::Cursor.new "#{feed_item.a_string}:#{feed_item.id}", field_name: 'a_string', field_type: String, include_current: true, type: :invalid
+      end.to raise_error Mongoid::Scroll::Errors::UnsupportedTypeError, /The type supplied in the cursor is not supported: invalid./
+    end
+  end
   context 'a cursor with include_current set to true' do
     let(:feed_item) { Feed::Item.create!(a_string: 'astring') }
     subject do