protected function assertHeaderValue($value)
    {
        if (!is_string($value) && (!is_array($value) || array_product(array_map('is_string', $value)) === 0)) {
            throw new \InvalidArgumentException("Header value should be a string or an array of strings");
        }
    }
protected function assertHeaderValue($value)
    {
        if (!is_string($value) && (!is_array($value) || array_product(array_map('is_string', $value)) === 0)) {
            throw new \InvalidArgumentException("Header value should be a string or an array of strings");
        }
    }
protected function assertHeaderValue ( $ value ) { if ( ! is_string ( $ value ) && ( ! is_array ( $ value ) || array_product ( array_map ( 'is_string' , $ value ) ) === 0 ) ) { throw new \ InvalidArgumentException ( "Header value should be a string or an array of strings" ) ; } }
Assert that the header value is a string

@param string|string[] $value
@throws \InvalidArgumentException
Assert that the header value is a string