NullInjectorError: No provider for Subscription!

[bobwatcherx]

i see tutorial and follow
for request my graphql url ,
i also add HttpClientModule in my angular App
, my console terminal no error , but i have error in console browser
like this

NullInjectorError: R3InjectorError(AppModule)[Subscription -> Subscription -> Subscription]:
NullInjectorError: No provider for Subscription!

whats wrong
my code : https://github.com/bobwatcherx/apolloangular.git
thanks