fix potential memory leak

[zhenghaoz]

No description provided.

[codecov-commenter]

Codecov Report

Merging #395 (9cc424a) into master (b566194) will increase coverage by 0.13%.
The diff coverage is 77.27%.

@@            Coverage Diff             @@
##           master     #395      +/-   ##
==========================================
+ Coverage   73.88%   74.01%   +0.13%     
==========================================
  Files          51       51              
  Lines       10273    10283      +10     
==========================================
+ Hits         7590     7611      +21     
+ Misses       1962     1955       -7     
+ Partials      721      717       -4     

Impacted Files	Coverage Δ
config/config.go	89.88% <ø> (ø)
server/rest.go	72.38% <50.00%> (+0.95%)	⬆️
master/tasks.go	58.90% <75.00%> (+0.14%)	⬆️
worker/worker.go	67.16% <80.64%> (-0.16%)	⬇️
base/heap/filter.go	100.00% <100.00%> (ø)
base/util.go	76.72% <100.00%> (+1.04%)	⬆️
storage/cache/database.go	88.88% <100.00%> (ø)
storage/cache/no_database.go	100.00% <100.00%> (ø)
storage/cache/redis.go	60.47% <100.00%> (+1.16%)	⬆️

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