NoMethodError when C32 file doesn't have patient element

[pelargir]

PatientImporter#get_demographics blows up at line 130 when the C32 file being parsed doesn't have a "ClinicalDocument > recordTarget > patientRole > patient" element:

NoMethodError: undefined method `at_xpath' for nil:NilClass
    /Users/pelargir/.rvm/gems/ruby-2.0.0-p0/gems/health-data-standards-3.1.1/lib/health-data-standards/import/c32/patient_importer.rb:130:in `get_demographics'
    /Users/pelargir/.rvm/gems/ruby-2.0.0-p0/gems/health-data-standards-3.1.1/lib/health-data-standards/import/c32/patient_importer.rb:86:in `parse_c32'

This should instead be handled gracefully without throwing an exception.