vb.net - "Value can not be null" on singleton instantiation -

i have singleton class attempting instantiate , giving exception "value cannot null"

im declaring reference in main form like:

dim devices deviceundertestbindinglist 

then instantiating in form.load:

devices = deviceundertestbindinglist.getinstance 

the deviceundertestbindinglist class follows:

imports system.componentmodel  public class deviceundertestbindinglist     ' deviceundertest 1 of other regular classes...     inherits system.componentmodel.bindinglist(of deviceundertest)      private shared singleinstance deviceundertestbindinglist     private shared instancelock object     private shared listlock object      private sub new()         mybase.new()     end sub      public shared readonly property getinstance deviceundertestbindinglist                     ' ensures 1 instance of list created.             if singleinstance nothing                 synclock (instancelock)                     if singleinstance nothing                         singleinstance = new deviceundertestbindinglist                     end if                 end synclock             end if             return singleinstance         end     end property end class 

i've used same pattern before no problems, of sudden causing exception, why?

please note: vb.net q! have read lot of c# q's deal similar problems did not understand them enough.

the problem cannot synclock on null variable. can synclock on valid instance of object. need change line:

private shared instancelock object 

to this:

private shared instancelock new object()