Fix values of false being converted to nil

Fixes #28

We previously checked for whether a hash value was truthy before setting
a default to nil. This meant that valid usages of a `false` value would
be ignored and set to nil.

Author: kevindew

lib/openapi3_parser/node_factory/object.rb

@@ -84,7 +84,7 @@ def build_data(raw_input)
 
       def process_data(raw_data)
         field_configs.each_with_object(raw_data.dup) do |(field, config), memo|
-          memo[field] = nil unless memo[field]
+          memo[field] = nil unless memo.key?(field)
           next unless config.factory?
 
           next_context = Context.next_field(context, field, memo[field])

spec/lib/openapi3_parser/node_factory/schema_spec.rb

@@ -120,6 +120,18 @@
     end
   end
 
+  describe "default field" do
+    it "supports a default field of false" do
+      node_factory_context = create_node_factory_context({ "default" => false })
+      node_context = node_factory_context_to_node_context(node_factory_context)
+
+      instance = described_class.new(node_factory_context)
+
+      expect(instance).to be_valid
+      expect(instance.node(node_context).default).to be(false)
+    end
+  end
+
   describe "validating writeOnly and readOnly" do
     it "is invalid when both writeOnly and readOnly are true" do
       instance = described_class.new(