Description of problem: Empty Text Box in service dialog causes error


Version-Release number of selected component (if applicable): 5.5.0.11


How reproducible: 100%


Steps to Reproduce:
1. Create a custom dialog for servicing with a single element, (Text Box)
2. Leave everything as default, so it is not required and has a default value of nothing.
3. Run a catalog provision using the dialog

Actual results: The provision fails, complaining it can't convert nil to String


Expected results: nil should be able to be converted to a String since the field is not required and the default can be blank.



Additional info:
[----] I, [2015-11-19T11:48:27.213802 #2938:7ef35d8]  INFO -- : Q-task_id([service_template_provision_task_23]) <AutomationEngine> <AEMethod dialog_parser> dialog_options: {"dialog_test"=>"", "request"=>"clone_to_service"}
[----] I, [2015-11-19T11:48:27.217110 #2938:7ef35d8]  INFO -- : Q-task_id([service_template_provision_task_23]) <AutomationEngine> <AEMethod dialog_parser> Current task has empty dialogs, getting dialog information from parent task
[----] E, [2015-11-19T11:48:27.219171 #2938:7ef35d8] ERROR -- : Q-task_id([service_template_provision_task_23]) <AutomationEngine> <AEMethod dialog_parser> The following error occurred during method evaluation:
[----] E, [2015-11-19T11:48:27.220432 #2938:7ef35d8] ERROR -- : Q-task_id([service_template_provision_task_23]) <AutomationEngine> <AEMethod dialog_parser>   TypeError: no implicit conversion of nil into String
[----] E, [2015-11-19T11:48:27.222479 #2938:7ef35d8] ERROR -- : Q-task_id([service_template_provision_task_23]) <AutomationEngine> <AEMethod dialog_parser>   /opt/rh/rh-ruby22/root/usr/share/gems/gems/psych-2.0.13/lib/psych.rb:370:in `parse'
/opt/rh/rh-ruby22/root/usr/share/gems/gems/psych-2.0.13/lib/psych.rb:370:in `parse_stream'
/opt/rh/rh-ruby22/root/usr/share/gems/gems/psych-2.0.13/lib/psych.rb:318:in `parse'
/opt/rh/rh-ruby22/root/usr/share/gems/gems/psych-2.0.13/lib/psych.rb:245:in `load'
<code: options_hash = YAML.load(bundle_task.get_option(:parsed_dialog_options))>:107:in `parent_task_dialog_information'