Add allow_nil: true option to the finder

README.md

@@ -104,6 +104,27 @@ existing users, do this from the console, runner, or add a Rake task:
 User.find_each(&:save)
 ```
 
+## Options
+
+### :allow_nil
+
+You can pass `allow_nil: true` to the `friendly.find()` method if you're want to
+avoid raising `ActiveRecord::RecordNotFound` and accept a `nil`.
+
+#### Example
+
+```ruby
+MyModel.friendly.find("bad-slug") # where bad-slug is not a valid slug
+MyModel.friendly.find(123)        # where 123 is not a valid primary key ID
+MyModel.friendly.find(nil)        # when you don't know if you even have a slug or ID
+#=> raise ActiveRecord::RecordNotFound
+
+MyModel.friendly.find("bad-slug", allow_nil: true) # where bad-slug is not a valid slug
+MyModel.friendly.find(123, allow_nil: true)        # where 123 is not a valid primary key ID
+MyModel.friendly.find(nil, allow_nil: true)        # when you don't know if you even have a slug or ID
+#=> nil
+```
+
 ## Bugs
 
 Please report them on the [Github issue

lib/friendly_id/finder_methods.rb

@@ -7,19 +7,31 @@ module FinderMethods
     # id matching '123' and then fall back to looking for a record with the
     # numeric id '123'.
     #
+    # @param [Boolean] allow_nil (default: false)
+    # Use allow_nil: true if you'd like the finder to return nil instead of
+    # raising ActivRecord::RecordNotFound
+    #
+    # ### Example
+    #
+    #     MyModel.friendly.find("bad-slug")
+    #     #=> raise ActiveRecord::RecordNotFound
+    #
+    #     MyModel.friendly.find("bad-slug", allow_nil: true)
+    #     #=> nil
+    #
     # Since FriendlyId 5.0, if the id is a nonnumeric string like '123-foo' it
     # will *only* search by friendly id and not fall back to the regular find
     # method.
     #
     # If you want to search only by the friendly id, use {#find_by_friendly_id}.
     # @raise ActiveRecord::RecordNotFound
-    def find(*args)
+    def find(*args, allow_nil: false)
       id = args.first
-      return super if args.count != 1 || id.unfriendly_id?
+      return super(*args) if args.count != 1 || id.unfriendly_id?
       first_by_friendly_id(id).tap { |result| return result unless result.nil? }
-      return super if potential_primary_key?(id)
+      return super(*args) if potential_primary_key?(id)
 
-      raise_not_found_exception(id)
+      raise_not_found_exception(id) unless allow_nil
     end
 
     # Returns true if a record with the given id exists.

test/finders_test.rb

@@ -25,4 +25,16 @@ def model_class
       assert model_class.existing.find(record.friendly_id)
     end
   end
+
+  test "allows nil with allow_nil: true" do
+    with_instance_of(model_class) do |record|
+      assert_nil model_class.find("foo", allow_nil: true)
+    end
+  end
+
+  test "allows nil on relations with allow_nil: true" do
+    with_instance_of(model_class) do |record|
+      assert_nil model_class.existing.find("foo", allow_nil: true)
+    end
+  end
 end