Switch parsejson() from PSON to JSON parsing

The use of PSON is deprecated and mostly removed from Puppet.
Switch this function from using PSON to a real JSON parsing
library via the MultiJson helper in Puppet::Util::Json.

Author: seanmil

lib/puppet/parser/functions/parsejson.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require 'puppet/util/json'
 #
 # parsejson.rb
 #
@@ -14,13 +15,14 @@ module Puppet::Parser::Functions
 
     > *Note:*
       The optional second argument can be used to pass a default value that will
-      be returned if the parsing of YAML string have failed.
+      be returned if the parsing of the JSON string failed or if the JSON parse
+      evaluated to nil.
   DOC
   ) do |arguments|
     raise ArgumentError, 'Wrong number of arguments. 1 or 2 arguments should be provided.' unless arguments.length >= 1
 
     begin
-      PSON.load(arguments[0]) || arguments[1]
+      Puppet::Util::Json.load(arguments[0]) || arguments[1]
     rescue StandardError => e
       raise e unless arguments[1]
       arguments[1]

spec/functions/parsejson_spec.rb

@@ -13,6 +13,14 @@
   end
 
   context 'with correct JSON data' do
+    it 'is able to parse JSON this is a null' do
+      is_expected.to run.with_params('null').and_return(nil)
+    end
+
+    it 'is able to parse JSON that is a string' do
+      is_expected.to run.with_params('"a string"').and_return('a string')
+    end
+
     it 'is able to parse JSON data with a Hash' do
       is_expected.to run.with_params('{"a":"1","b":"2"}')
                         .and_return('a' => '1', 'b' => '2')
@@ -49,16 +57,16 @@
 
   context 'with incorrect JSON data' do
     it 'raises an error with invalid JSON and no default' do
-      is_expected.to run.with_params('')
-                        .and_raise_error(PSON::ParserError)
+      is_expected.to run.with_params('error')
+                        .and_raise_error(Puppet::Util::Json::ParseError)
     end
 
     it 'supports a structure for a default value' do
       is_expected.to run.with_params('', 'a' => '1')
                         .and_return('a' => '1')
     end
 
-    ['', 1, 1.2, nil, true, false, [], {}, :yaml].each do |value|
+    [1, 1.2, nil, true, false, [], {}, :yaml].each do |value|
       it "returns the default value for an incorrect #{value.inspect} (#{value.class}) parameter" do
         is_expected.to run.with_params(value, 'default_value')
                           .and_return('default_value')