src/validate.js
function validateHeader (key, value) {
  if (typeof key !== 'string' || typeof value !== 'string')
    return option.some(`Parts of header ${key}:${value} must be strings`)
  return option.none
}
function validateHeader (key, value) {
  if (typeof key !== 'string' || typeof value !== 'string')
    return option.some(`Parts of header ${key}:${value} must be strings`)
  return option.none
}
function validateHeader ( key , value ) { if ( typeof key !== 'string' || typeof value !== 'string' ) return option . some ( ` ${ key } ${ value } ` ) return option . none }
Validate header to all parts be strings
@param {String} key – Header key
@param {String} value – Header value
@return {String} error
Validate header to all parts be strings