omit empty value in dumped JSON

[davies]

No description provided.

[codecov-commenter]

Codecov Report

Merging #1676 (5f5d200) into main (6f4200f) will decrease coverage by 0.08%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #1676      +/-   ##
==========================================
- Coverage   61.80%   61.72%   -0.09%     
==========================================
  Files         133      134       +1     
  Lines       22607    22648      +41     
==========================================
+ Hits        13973    13979       +6     
- Misses       7074     7099      +25     
- Partials     1560     1570      +10     

Impacted Files	Coverage Δ
pkg/meta/dump.go	73.84% <0.00%> (-1.75%)	⬇️
pkg/utils/utils_unix.go	42.85% <0.00%> (-42.86%)	⬇️
pkg/vfs/reader.go	81.56% <0.00%> (-4.38%)	⬇️
pkg/object/file.go	64.68% <0.00%> (-0.84%)	⬇️
pkg/chunk/cached_store.go	78.51% <0.00%> (-0.20%)	⬇️
pkg/meta/sql.go	67.28% <0.00%> (-0.11%)	⬇️
pkg/meta/tkv.go	76.62% <0.00%> (-0.06%)	⬇️
pkg/meta/redis.go	73.04% <0.00%> (ø)
pkg/object/object_storage.go	76.78% <0.00%> (ø)
pkg/utils/utils_linux.go	0.00% <0.00%> (ø)
... and 2 more

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