Merge pull request #2980 from Kaligo/bugfix/display_empty_json

Fixed displaying empty json in edit form

Author: mshibuya

lib/rails_admin/config/fields/types/json.rb

@@ -10,7 +10,7 @@ class Json < RailsAdmin::Config::Fields::Types::Text
           RailsAdmin::Config::Fields::Types.register(:jsonb, self)
 
           register_instance_option :formatted_value do
-            value.present? ? JSON.pretty_generate(value) : nil
+            value ? JSON.pretty_generate(value) : nil
           end
 
           register_instance_option :pretty_value do

spec/rails_admin/config/fields/types/json_spec.rb

@@ -19,6 +19,12 @@
       end
     end
 
+    it 'returns correct value for empty json' do
+      allow(object).to receive(:json_field) { {} }
+      actual = field.with(bindings).formatted_value
+      expect(actual).to eq("{\n}")
+    end
+
     it 'retuns correct value' do
       allow(object).to receive(:json_field) { {sample_key: "sample_value"} }
       actual = field.with(bindings).formatted_value