error field has extra not needed and not documented array

[matkoniecz]

see also #128

To reproduce: enable config={{"header": true}}

Pass data where some rows have less columns than header

[[{"type":"FieldMismatch","code":"TooFewFields","message":"Too few fields: expected 10 fields but parsed 1","row":7}],[{"type":"FieldMismatch","code":"TooFewFields","message":"Too few fields: expected 10 fields but parsed 1","row":8}],[{"type":"FieldMismatch","code":"TooFewFields","message":"Too few fields: expected 10 fields but parsed 1","row":9}],[{"type":"FieldMismatch","code":"TooFewFields","message":"Too few fields: expected 10 fields but parsed 1","row":10}],[{"type":"FieldMismatch","code":"TooFewFields","message":"Too few fields: expected 10 fields but parsed 1","row":11}],[{"type":"FieldMismatch","code":"TooFewFields","message":"Too few fields: expected 10 fields but parsed 1","row":12}],[{"type":"FieldMismatch","code":"TooFewFields","message":"Too few fields: expected 10 fields but parsed 1","row":13}],[{"type":"FieldMismatch","code":"TooFewFields","message":"Too few fields: expected 10 fields but parsed 1","row":14}]]

why each error is packed into a single element array?