Column without a header

One or more columns of an uploaded file have no header. A column without a name cannot be mapped to a field, so later steps cannot reach its values. The file is still stored; this is a warning.

What to do

Add a header to each blank column, or remove the column, and upload the file again. The message gives the position of each blank column.

Where it comes from

Shown by Import Data. It is one of the messages about a node.