Fix for as_symbols=true when command is nothing

[carlobaldassi]

Fix #100

[codecov-io]

Codecov Report

Merging #102 (fc537b9) into master (92764f2) will decrease coverage by 0.20%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #102      +/-   ##
==========================================
- Coverage   95.92%   95.71%   -0.21%     
==========================================
  Files           5        5              
  Lines        1201     1283      +82     
==========================================
+ Hits         1152     1228      +76     
- Misses         49       55       +6     

Impacted Files	Coverage Δ
src/parsing.jl	96.73% <100.00%> (-0.18%)	⬇️
src/settings.jl	96.48% <0.00%> (-0.21%)	⬇️
src/deprecated.jl	0.00% <0.00%> (ø)

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