Update error messages

[Kb-Tay]

No description provided.

[codecov]

Codecov Report

Merging #154 (8d53efe) into master (b06dbdc) will not change coverage.
Report is 15 commits behind head on master.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #154   +/-   ##
=========================================
  Coverage     75.61%   75.61%           
  Complexity      662      662           
=========================================
  Files           101      101           
  Lines          2149     2149           
  Branches        222      222           
=========================================
  Hits           1625     1625           
  Misses          461      461           
  Partials         63       63           

Files	Coverage Δ
.../seedu/address/logic/commands/ScheduleCommand.java	61.29% <ø> (ø)
...java/seedu/address/logic/commands/SortCommand.java	100.00% <ø> (ø)
...java/seedu/address/model/person/NextOfKinName.java	100.00% <ø> (ø)

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[jylow]

Thanks for fixing the bugs!