This diff fixes a bug when the option in the config file provided, but has an empty value the app throws the following error:
`what(): basic_string::_M_construct null not valid`.
To fix this we will check the option value not to be empty or throw an appropriate error.
Linear task: [[ https://linear.app/comm/issue/ENG-1059/handle-condition-when-the-tunnelbroker-config-option-is-empty | ENG-1059 ]]