Fetching Environment Variable with Existence Check - Golang

Fetching a specific environment var from execution environment (where Go program is running) is little trick as Go provide 2 methods/function for that. Choose the function based on the requirement.  

os.Getenv
  This function will return value if Env var exists or return empty string if not. So it is difficult to gather if Env var value is empty or Env var is not exists. 

os.LookupEnv
  To overcome above problem, this function will check if Env var existence and return either value or the error. 

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