src/RequestOptions/RequestOptions.php
public function addDefaultHeader($name, $value)
    {
        if (!isset($this->headers[$name])) {
            $this->headers[$name] = $value;
        }

        return $this;
    }
public function addDefaultHeader($name, $value)
    {
        if (!isset($this->headers[$name])) {
            $this->headers[$name] = $value;
        }

        return $this;
    }
public function addDefaultHeader ( $ name , $ value ) { if ( ! isset ( $ this -> headers [ $ name ] ) ) { $ this -> headers [ $ name ] = $ value ; } return $ this ; }
Add a new header to the list if there is no value already set.

@param string $name  Name of the header
@param string $value Value of the header

@return $this
Add a new header to the list if there is no value already set .