code: def valid_credentials?
        return false unless api_key?
        !activities.all.nil?
      rescue Rescuetime::Errors::InvalidCredentialsError
        false
      end
docs: Returns true if the provided api key is valid. Performs a request to the
   Rescuetime API.
  
   @example Basic Use
     # Assuming that INVALID_KEY is an invalid Rescuetime API key
     # and VALID_KEY is a valid one
  
     client = Rescuetime::Client
     client.valid_credentials?
     # => false
  
     client.api_key = INVALID_KEY
     client.valid_credentials? # Performs a request to the Rescuetime API
     # => false
  
     client.api_key = VALID_KEY
     client.valid_credentials? # Performs a request to the Rescuetime API
     # => true
  
   @return [Boolean]