json resource: ensure params is not nil in even of read/parse failure (#2354)

When the JSON resource (and those that subclass off of it) were modified
to properly throw exceptions in the event of failure, this caused the
`params` method to return nil instead of what it used to be, an empty
hash.

This is fine in the case of a describe block, but it's not okay when used
outside of a describe, as it will cause users trying to pluck from the
hash to throw a dreaded-and-unhelpful NilClass error.

This change pre-populates the params to be an empty hash, and if the
read/parse steps fail, it will still be one.

Signed-off-by: Adam Leff <adam@leff.co>

lib/resources/json.rb

@@ -29,6 +29,12 @@ module Inspec::Resources
     attr_reader :params, :raw_content
 
     def initialize(opts)
+      # pre-initialize @params to an empty hash. In the event that reading/parsing the data
+      # throws an exception, this allows the resource to still be called outside of a
+      # describe/test and not throw errors when a caller attempts to fetch a value from the params.
+      @params = {}
+
+      # load the raw content from the source, and then parse it
       @raw_content = load_raw_content(opts)
       @params = parse(@raw_content)
     end

test/unit/resources/json_test.rb

@@ -33,12 +33,17 @@ describe 'Inspec::Resources::JSON' do
       _(resource.send(:'x.y.z')).must_be_nil
     end
   end
+
   describe 'when loading a nonexistent file' do
-    let (:resource) { load_resource('json', 'nonexistent.json') }
+    let(:resource) { load_resource('json', 'nonexistent.json') }
 
     it 'produces an error' do
       _(resource.resource_exception_message).must_equal 'No such file: nonexistent.json'
     end
+
+    it 'still provides an empty hash for params' do
+      _(resource.params).must_equal({})
+    end
   end
 
   describe '#load_raw_from_file' do