Fix bugs related to error messages

[yanghengtang]

Closes #299 Closes #300

[codecov[bot]]

Codecov Report

Merging #301 (b259d74) into master (c7efd98) will increase coverage by 80.69%. Report is 9 commits behind head on master. The diff coverage is n/a.

@@              Coverage Diff              @@
##             master     #301       +/-   ##
=============================================
+ Coverage          0   80.69%   +80.69%     
- Complexity        0      940      +940     
=============================================
  Files             0      137      +137     
  Lines             0     2839     +2839     
  Branches          0      277      +277     
=============================================
+ Hits              0     2291     +2291     
- Misses            0      513      +513     
- Partials          0       35       +35     

Files	Coverage Δ
...ess/logic/commands/AddMedicalConditionCommand.java	100.00% <ø> (ø)
...address/logic/commands/AddPrescriptionCommand.java	100.00% <ø> (ø)
...dress/logic/commands/AddSpecialisationCommand.java	100.00% <ø> (ø)
...dress/logic/commands/AppointmentRemarkCommand.java	100.00% <ø> (ø)
.../logic/commands/DeleteMedicalConditionCommand.java	100.00% <ø> (ø)
...ress/logic/commands/DeletePrescriptionCommand.java	100.00% <ø> (ø)
...ss/logic/commands/DeleteSpecialisationCommand.java	100.00% <ø> (ø)
...du/address/logic/commands/DoctorRemarkCommand.java	100.00% <ø> (ø)
...address/logic/commands/EditAppointmentCommand.java	97.40% <ø> (ø)
...eedu/address/logic/commands/EditDoctorCommand.java	96.61% <ø> (ø)
... and 2 more

... and 125 files with indirect coverage changes

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