Getting an "Invalid date" error when structure element is empty/null

I've ran into an issue where I'm referencing a field in a structure (which is of type date) that gives a error when it's not populated, but works fine when it's been set.

Am I using the library correctly? Or is this s bug?

I've ran the code below in IRB:

require 'nwrfc'
include NWRFC

SAP_USER = 'user'
SAP_PASS = "***pass**" 

SAP_HOST = "172.17.x.x"
SAP_SYSNR = "00"
SAP_MANDT = "300"

connection = Connection.new( {
    'user' => SAP_USER, 
    "passwd" => SAP_PASS, 
    "client" => SAP_MANDT, 
    "ashost" => SAP_HOST, 
    "sysnr" => SAP_SYSNR })

function = connection.get_function("BAPI_USER_GET_DETAIL")
fc = function.get_function_call
fc[:USERNAME]="INACTIVEUSER"
fc.invoke
# Works fine when called on an inactive user (where "valid to" date is set)
fc[:LOGONDATA][:GLTGB] #  => #<Date: 2011-06-13 ((2455726j,0s,0n),+0s,2299161j)>
fc[:LOGONDATA][:GLTGB].to_s  #  => "2011-06-13"

# Metadata for field:
 fc[:LOGONDATA].member_metadata :GLTGB
# => {:name=>"GLTGB", :type=>:RFCTYPE_DATE, :nucLength=>8, :ucLength=>16, :decimals=>0, :typeDescHandle=>#<FFI::Pointer address=0x00000000000000>}

# Now call for an ACTIVE user (where the :GLBTB entry is not yet populated)
fc[:USERNAME]="ACTIVEUSER"
fc.invoke

fc[:LOGONDATA][:GLTGB].to_s
# BOOM!
ArgumentError: invalid date
        from /home/vagrant/.rvm/gems/ruby-2.2.5/gems/nwrfc-0.0.9/lib/nwrfc/datacontainer.rb:43:in `parse'
        from /home/vagrant/.rvm/gems/ruby-2.2.5/gems/nwrfc-0.0.9/lib/nwrfc/datacontainer.rb:43:in `[]'
        from (irb):70
        from /home/vagrant/.rvm/rubies/ruby-2.2.5/bin/irb:11:in `<main>'

# Other fields which are set return correct data:
fc[:LOGONDATA][:LTIME].to_s # "2017-08-05 10:48:11 +0000"

mydoghasworms / nwrfc

Getting an "Invalid date" error when structure element is empty/null #10