Improve code quality

[yongxiangng]

No description provided.

[codecov-commenter]

Codecov Report

Merging #171 (57db4cf) into master (f96b2ab) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #171   +/-   ##
=========================================
  Coverage     70.51%   70.51%           
  Complexity      613      613           
=========================================
  Files            95       95           
  Lines          1899     1899           
  Branches        245      245           
=========================================
  Hits           1339     1339           
  Misses          461      461           
  Partials         99       99           

Impacted Files	Coverage Δ
src/main/java/seedu/address/model/AddressBook.java	88.63% <ø> (ø)
src/main/java/seedu/address/model/event/Event.java	75.00% <ø> (ø)
...a/seedu/address/logic/commands/DetailsCommand.java	84.21% <100.00%> (ø)

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