Get String Not Allowed To Be Called from Mono Behaviour Constructor

What does this even mean and how can it be fixed? We need to be able to set a string into player prefs for users to use their own serial port configuration?

 GetString is not allowed to be called from a MonoBehaviour constructor (or instance field initializer), call it in Awake or Start instead. Called from MonoBehaviour 'Sending'.
 See "Script Serialization" page in the Unity Manual for further details.
 UnityEngine.PlayerPrefs:GetString(String)
 Sending:.cctor()