Error Message Does Not Match When Using Invalid Optional Command Formats

[ZaydM18]

Steps to Reproduce:

1. Type out a full valid add command without any optional parameters, e.g., add n/Betsy Crowe dob/01/01/2001 t/friend e/betsycrowe@example.com a/Newgate Prison p/1234567 t/NoFamily mh/Insane, but not dangerous b/B+ ap/Patient
2. Type out a (reasonable) invalid command parameter (such as tag/ or email/).

Expected: Invalid Command Format Message
Actual: Incorrect Command Constraint Message (i.e., "This does not fit the requirements for the last valid parameter.").

It would be better to handle this special case of incorrect command formats by displaying the standard invalid command message.