docstr: Workflow used to test optional string parameters in the
  introspective argument parser.
  
  Parameters
  ----------
  optional_str_1 : variable str, optional
      optional string argument 1
  optional_str_2 : str, optional
      optional string argument 2 (default 'default')
docstr_tok: ["Workflow","used","to","test","optional","string","parameters","in","the","introspective","argument","parser",".","Parameters","--","--","--","--","--","optional_str_1",":","variable","str",",","optional","optional","string","argument","1","optional_str_2",":","str",",","optional","optional","string","argument","2","(","default","'default","'",")"]
code: def run(self, optional_str_1=None, optional_str_2="default"):
      """Workflow used to test optional string parameters in the
      introspective argument parser.
  
      Parameters
      ----------
      optional_str_1 : variable str, optional
          optional string argument 1
      optional_str_2 : str, optional
          optional string argument 2 (default 'default')
      """
      return optional_str_1, optional_str_2
  
imports: from dipy.workflows.workflow import Workflow
  from dipy.workflows.combined_workflow import CombinedWorkflow
label_desc: Use image node_id 1 for calling the DummyWorkflowOptionalStr obj's underlying member method code with example usage: obj.run(optional_str_1, optional_str_2) and returns: optional_str_1,  optional_str_2