The length validator only takes effect for parameters with types th…

…at support `#length` method

CHANGELOG.md

@@ -3,6 +3,7 @@
 #### Features
 
 * [#2475](https://github.com/ruby-grape/grape/pull/2475): Remove Grape::Util::Registrable - [@ericproulx](https://github.com/ericproulx).
+* [#2464](https://github.com/ruby-grape/grape/pull/2464): The `length` validator only takes effect for parameters with types that support `#length` method - [@OuYangJinTing](https://github.com/OuYangJinTing).
 * Your contribution here.
 
 #### Fixes

lib/grape/validations/validators/length_validator.rb

@@ -18,7 +18,7 @@ def initialize(attrs, options, required, scope, **opts)
         def validate_param!(attr_name, params)
           param = params[attr_name]
 
-          raise ArgumentError, "parameter #{param} does not support #length" unless param.respond_to?(:length)
+          return unless param.respond_to?(:length)
 
           return unless (!@min.nil? && param.length < @min) || (!@max.nil? && param.length > @max)
 

spec/grape/validations/validators/length_spec.rb

@@ -81,6 +81,12 @@
       post 'zero_max' do
       end
 
+      params do
+        requires :list, type: [Integer], length: { min: 2 }
+      end
+      post 'nil_param' do
+      end
+
       params do
         requires :list, type: [Integer], length: { min: 2, message: 'not match' }
       end
@@ -187,6 +193,16 @@
     end
   end
 
+  describe '/nil_param' do
+    context 'does not raise an error' do
+      it do
+        expect do
+          post '/nil_param', list: nil
+        end.not_to raise_error
+      end
+    end
+  end
+
   describe '/type_is_not_array' do
     context 'raises an error' do
       it do