Error in building

[favera]

Hi, when i upload files .xls give me this error
index.js:29815 TypeError: Cannot convert undefined or null to object at Function.keys (<anonymous>) at a.xlsxArrToTableArr (index.js:29870) at a.n [as xlsxArrToTableArr] (vue.esm.js:188) at index.js:29813 at <anonymous>
the line in index.js is this
var tableHeader = Object.keys(xlsxArr[maxLengthIndex]);