Fix: panic: assignment to entry in nil map

[k1LoW]

panic: assignment to entry in nil map

goroutine 1 [running]:
github.com/k1LoW/tbls/output/config.(*Config).OutputSchema(0xc0000d8860, 0x4bf39e0, 0xc0000d8868, 0xc0005b54a0, 0x0, 0x0)
        /Users/k1low/src/github.com/k1LoW/tbls/output/config/config.go:46 +0xbe7
github.com/k1LoW/tbls/cmd.glob..func4(0x5276e00, 0xc000049180, 0x0, 0x4)
        /Users/k1low/src/github.com/k1LoW/tbls/cmd/out.go:122 +0x22e
github.com/spf13/cobra.(*Command).execute(0x5276e00, 0xc000049140, 0x4, 0x4, 0x5276e00, 0xc000049140)
        /Users/k1low/go/pkg/mod/github.com/spf13/[email protected]/command.go:830 +0x2aa
github.com/spf13/cobra.(*Command).ExecuteC(0x5277080, 0x0, 0x0, 0x0)
        /Users/k1low/go/pkg/mod/github.com/spf13/[email protected]/command.go:914 +0x2fb
github.com/spf13/cobra.(*Command).Execute(...)
        /Users/k1low/go/pkg/mod/github.com/spf13/[email protected]/command.go:864
github.com/k1LoW/tbls/cmd.Execute()
        /Users/k1low/src/github.com/k1LoW/tbls/cmd/root.go:59 +0x2d
main.main()
        /Users/k1low/src/github.com/k1LoW/tbls/main.go:33 +0x20
make: *** [db/doc] Error 2

[codecov]

Codecov Report

Merging #147 into master will decrease coverage by 1.21%.
The diff coverage is 9.09%.

@@            Coverage Diff             @@
##           master     #147      +/-   ##
==========================================
- Coverage   70.06%   68.85%   -1.22%     
==========================================
  Files          13       13              
  Lines        2789     2793       +4     
==========================================
- Hits         1954     1923      -31     
- Misses        638      679      +41     
+ Partials      197      191       -6

Impacted Files	Coverage Δ
output/config/config.go	48.33% <9.09%> (-3.46%)	⬇️
datasource/datasource.go	20.85% <0%> (-19.02%)	⬇️

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