(CAT-1724) - Fix Provider returned data not matching Type Schema

Prior to this commit, we would see the above error returned when dsc
would return a nil value for a required string in its data hash.

As puppet is not expecting a nil value, but rather an empty string, the
error is raised on each puppet run where this occurs.

We can fix this by converting all required string attributes values in
the data hash from nil to an empty string ('').

Author: jordanbreen28

lib/puppet/provider/dsc_base_provider/dsc_base_provider.rb

@@ -351,7 +351,7 @@ def insync?(context, name, _property_name, _is_hash, should_hash)
   # @param context [Object] the Puppet runtime context to operate in and send feedback to
   # @param name_hash [Hash] the hash of namevars to be passed as properties to `Invoke-DscResource`
   # @return [Hash] returns a hash representing the DSC resource munged to the representation the Puppet Type expects
-  def invoke_get_method(context, name_hash)
+  def invoke_get_method(context, name_hash) # rubocop:disable Metrics/AbcSize
     context.debug("retrieving #{name_hash.inspect}")
 
     query_props = name_hash.select { |k, v| mandatory_get_attributes(context).include?(k) || (k == :dsc_psdscrunascredential && !v.nil?) }
@@ -394,6 +394,8 @@ def invoke_get_method(context, name_hash)
     # If a resource is found, it's present, so refill this Puppet-only key
     data[:name] = name_hash[:name]
 
+    data = stringify_nil_attributes(context, data)
+
     # Have to check for this to avoid a weird canonicalization warning
     # The Resource API calls canonicalize against the current state which
     # will lead to dsc_ensure being set to absent in the name_hash even if
@@ -663,6 +665,20 @@ def mandatory_set_attributes(context)
     context.type.attributes.select { |_attribute, properties| properties[:mandatory_for_set] }.keys
   end
 
+  # Parses the DSC resource type definition to retrieve the names of any attributes which are specifed as required strings
+  # This is used to ensure that any nil values are converted to empty strings to match the DSC behaviour
+  # @param context [Object] the Puppet runtime context to operate in and send feedback to
+  # @param data [Hash] the hash of properties returned from the DSC resource
+  # @return [Hash] returns a data hash with any nil values converted to empty strings
+  def stringify_nil_attributes(context, data)
+    nil_strings = data.select { |_name, value| value.nil? }.keys
+    string_attrs = context.type.attributes.select { |_name, properties| properties[:type] == 'String' }.keys
+    string_attrs.each do |attribute|
+      data[attribute] = '' if nil_strings.include?(attribute)
+    end
+    data
+  end
+
   # Parses the DSC resource type definition to retrieve the names of any attributes which are specified as namevars
   #
   # @param context [Object] the Puppet runtime context to operate in and send feedback to