Add is_a?(Array) to coerce_nil because of Array with a type.

Add CHANGELOG.md

Author: ericproulx

CHANGELOG.md

@@ -9,6 +9,7 @@
 #### Fixes
 
 * Your contribution here.
+* [#2040](https://github.com/ruby-grape/grape/pull/2040): Fix a regression with Array of type nil - [@ericproulx](https://github.com/ericproulx).
 
 ### 1.3.2 (2020/04/12)
 

lib/grape/validations/validators/coerce.rb

@@ -76,7 +76,7 @@ def coerce_value(val)
       def coerce_nil(val)
         # define default values for structures, the dry-types lib which is used
         # for coercion doesn't accept nil as a value, so it would fail
-        return []      if type == Array
+        return []      if type == Array || type.is_a?(Array)
         return Set.new if type == Set
         return {}      if type == Hash
         val

spec/grape/validations/validators/coerce_spec.rb

@@ -311,6 +311,22 @@ def self.parsed?(value)
           expect(last_response.status).to eq(400)
           expect(last_response.body).to eq('uri is invalid')
         end
+
+        context 'Array of types nil' do
+          it 'Empty array' do
+            subject.params do
+              requires :arry, type: Array[Integer]
+            end
+            subject.get '/array' do
+              params[:arry]
+            end
+
+            get '/array', arry: nil
+            expect(last_response.status).to eq(200)
+            expect(last_response.body).to eq('[]')
+          end
+        end
+
       end
 
       context 'Set' do