Make json the default string representation

For Product, Resource and type override the to_s so that it will return pretty
json instead of the name of the class.

api/product.rb

@@ -34,6 +34,10 @@ def api_name
       name.downcase
     end
 
+    def to_s
+      JSON.pretty_generate(self)
+    end
+
     def to_json(opts = nil)
       json_out = {}
 

api/resource.rb

@@ -135,6 +135,10 @@ def validate
       end
     end
 
+    def to_s
+      JSON.pretty_generate(self)
+    end
+
     def to_json(opts = nil)
       # ignore fields that will contain references to parent resources
       ignored_fields = %i[@__product @__parent @__resource @api_name @collection_url_response]

api/type.rb

@@ -83,7 +83,7 @@ def to_json(opts = nil)
       instance_variables.each do |v|
         if v == :@conflicts && instance_variable_get(v).empty?
           # ignore empty conflict arrays
-        elsif instance_variable_get(v) == false
+        elsif instance_variable_get(v) == false || instance_variable_get(v).nil?
           # ignore false booleans as non-existence indicates falsey
         elsif !ignored_fields.include? v
           json_out[v] = instance_variable_get(v)