skip validation for a file if it is optional and nil (#1977)

Author: dnesteryuk

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 #### Fixes
 
+* [#1977](https://github.com/ruby-grape/grape/pull/1977): Skip validation for a file if it is optional and nil - [@dnesteryuk](https://github.com/dnesteryuk).
 * [#1976](https://github.com/ruby-grape/grape/pull/1976): Ensure classes/modules listed for autoload really exist - [@dnesteryuk](https://github.com/dnesteryuk).
 * [#1971](https://github.com/ruby-grape/grape/pull/1971): Fix BigDecimal coercion - [@FlickStuart](https://github.com/FlickStuart).
 * [#1968](https://github.com/ruby-grape/grape/pull/1968): Fix args forwarding in Grape::Middleware::Stack#merge_with for ruby 2.7.0 - [@dm1try](https://github.com/dm1try).

lib/grape/validations/types/file.rb

@@ -8,6 +8,7 @@ module Types
       # this class is here only to assert that rack's handling has succeeded.
       class File
         def call(input)
+          return if input.nil?
           return InvalidValue.new unless coerced?(input)
 
           # Processing of multipart file objects

spec/grape/validations_spec.rb

@@ -11,14 +11,17 @@ def app
 
   describe 'params' do
     context 'optional' do
-      it 'validates when params is present' do
+      before do
         subject.params do
           optional :a_number, regexp: /^[0-9]+$/
+          optional :attachment, type: File
         end
         subject.get '/optional' do
           'optional works!'
         end
+      end
 
+      it 'validates when params is present' do
         get '/optional', a_number: 'string'
         expect(last_response.status).to eq(400)
         expect(last_response.body).to eq('a_number is invalid')
@@ -29,14 +32,7 @@ def app
       end
 
       it "doesn't validate when param not present" do
-        subject.params do
-          optional :a_number, regexp: /^[0-9]+$/
-        end
-        subject.get '/optional' do
-          'optional works!'
-        end
-
-        get '/optional'
+        get '/optional', a_number: nil, attachment: nil
         expect(last_response.status).to eq(200)
         expect(last_response.body).to eq('optional works!')
       end