To successfully run this app put your api key at

app -> src -> main -> res -> values -> strings.xml

in 

<string name="api_key"></string>

tab

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To get key ,  use the API from themoviedb.org.
If you don’t already have an account, you will need to create one in order to request an API Key.


signup at -  https://www.themoviedb.org/account/signup

to register and get key