Fix bugs in logic classes

[teozhengyang]

Edit commands and parsers classes (Add/Remove Event/Schedule) and their related test cases due to bugs

[andrefoo]

LGTM!

[codecov]

Codecov Report

Merging #247 (00b4d89) into master (288c2b7) will increase coverage by 8.71%.
Report is 9 commits behind head on master.
The diff coverage is 62.72%.

@@             Coverage Diff              @@
##             master     #247      +/-   ##
============================================
+ Coverage     66.82%   75.54%   +8.71%     
- Complexity      815      914      +99     
============================================
  Files           111      111              
  Lines          2900     2911      +11     
  Branches        329      340      +11     
============================================
+ Hits           1938     2199     +261     
+ Misses          896      624     -272     
- Partials         66       88      +22     

Files	Coverage Δ
.../address/logic/commands/CommonFreetimeCommand.java	66.12% <ø> (+55.98%)	⬆️
...du/address/logic/parser/AddEventCommandParser.java	100.00% <100.00%> (+100.00%)	⬆️
...address/logic/parser/AddScheduleCommandParser.java	100.00% <100.00%> (+100.00%)	⬆️
...address/logic/parser/RemoveEventCommandParser.java	100.00% <100.00%> (+100.00%)	⬆️
...ress/logic/parser/RemoveScheduleCommandParser.java	100.00% <100.00%> (+100.00%)	⬆️
...main/java/seedu/address/model/person/Birthday.java	100.00% <ø> (ø)
...seedu/address/model/person/timetable/Schedule.java	93.41% <100.00%> (+9.67%)	⬆️
...eedu/address/model/person/timetable/TimeBlock.java	97.22% <ø> (+41.40%)	⬆️
.../java/seedu/address/model/util/SampleDataUtil.java	16.66% <ø> (+2.38%)	⬆️
src/main/java/seedu/address/model/AddressBook.java	95.23% <0.00%> (+2.38%)	⬆️
... and 4 more

... and 4 files with indirect coverage changes

[kristayeo]

LGTM