Fix type warning

[bernarduskrishna]

No description provided.

[codecov-commenter]

Codecov Report

Merging #224 (0d4e522) into master (0fa7b7d) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #224   +/-   ##
=========================================
  Coverage     80.15%   80.15%           
  Complexity      836      836           
=========================================
  Files            99       99           
  Lines          2167     2167           
  Branches        305      305           
=========================================
  Hits           1737     1737           
  Misses          343      343           
  Partials         87       87           

Impacted Files	Coverage Δ
...main/java/seedu/address/model/TransactionList.java	100.00% <100.00%> (ø)

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