fix merging empty entry table

[codecov[bot]]

Codecov Report

Merging #404 (7a7af9d) into master (b8a0cb2) will increase coverage by 0.18%. The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master     #404      +/-   ##
==========================================
+ Coverage   89.16%   89.35%   +0.18%     
==========================================
  Files          73       73              
  Lines        4449     4452       +3     
==========================================
+ Hits         3967     3978      +11     
+ Misses        482      474       -8     

Impacted Files	Coverage Δ
lib/YaoBlocks/src/composite/chain.jl	95.41% <ø> (ø)
lib/YaoBlocks/src/composite/control.jl	97.95% <ø> (ø)
lib/YaoBlocks/src/composite/kron.jl	95.12% <ø> (ø)
lib/YaoBlocks/src/composite/put_block.jl	100.00% <ø> (ø)
lib/YaoBlocks/src/composite/unitary_channel.jl	100.00% <ø> (ø)
lib/YaoBlocks/src/primitive/rotation_gate.jl	96.07% <ø> (ø)
lib/YaoBlocks/src/primitive/shift_gate.jl	90.00% <ø> (ø)
lib/YaoBlocks/src/primitive/time_evolution.jl	94.33% <ø> (ø)
lib/YaoBlocks/src/routines.jl	96.00% <66.66%> (+0.01%)	:arrow_up:
lib/YaoBlocks/src/abstract_block.jl	89.58% <100.00%> (+0.05%)	:arrow_up:
... and 3 more

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[GiggleLiu]

I will merge first, you can still review later.