Error message for undefined parameters

[abhsarma]

Currently the error messages for a parameter which has not been defined yet is unintuitive. Consider:

df = data.raw.study2 %>%
    mutate( ComputedCycleLength = StartDateofLastPeriod - StartDateofPeriodBeforeLast ) %>%
    mutate(NextMenstrualOnset = branch(menstrual_calculation,
        "mc_option1" %when% (cycle_length != "cl_option3") ~ StartDateofLastPeriod + ComputedCycleLength,
        "mc_option2" %when% (cycle_length != "cl_option2") ~ StartDateofLastPeriod + ReportedCycleLength,
        "mc_option3" ~ StartDateNext)
    )

If the cycle_length parameter has not been defined previously, then we correctly get an error message, but the message is not intuitive and the message is only displayed in the console (not underneath the code block):

• [x] improve the message
• [x] duplicate the error with code blocks
• [x] inspect how error is displayed with inside
• [x] display error below the code block