Returns the value of the first header by the given case-insensitive name, or null if no such header is present.

@param string $name

@return string|null
767984
public function getFirstHeader(string $name) : ?string
    {
        $name = strtolower($name);

        return isset($this->headers[$name]) ? reset($this->headers[$name]) : null;
    }
878430
public function first($name)
    {
        if (isset($this->files[$name])) {
            return $this->files[$name];
        }

        foreach ($this->files as $key => $file) {
            if (strpos($key, "{$name}[") === 0) {
                return $file;
            }
        }
    }
859326
public function getHeader( $name ) {
		$this->initHeaders();
		$name = strtoupper( $name );
		if ( !isset( $this->headers[$name] ) ) {
			return false;
		}
		return $this->headers[$name];
	}
794137
public function getStringValue($name):?string
    {
        $value = $this->offsetGet($name);
        if (is_null($value)) {
            return null;
        }

        return (string)$value;
    }
1180935
public function findValueByName($name)
    {
        // No values defined yet.
        if (is_null($this->values)) {
            return null;
        }

        // Traverse and Return.
        return $this->traverseNodesAndFindBy('name', $name, $this->values);
    }
865785
public final function header(string $name, string $value = null)
    {
        return ($value === null) ? $this->getHeader($name) : $this->setHeader($name, $value);
    }
305284
protected function header(string $name)
    {
        return isset($this->request->getHeaders()[$name]) ?
            $this->request->getHeaders()[$name][0] : null;
    }
1304981
public function getHeader($name) {
        if (!is_string($name)) throw new IllegalTypeException('Illegal type of parameter $name: '.gettype($name));
        if (!strlen($name))    throw new InvalidArgumentException('Invalid argument $name: '.$name);

        $headers = $this->getHeaders($name);
        if ($headers)
            return join(', ', $headers);    // combine multiple headers of the same name according to RFC
        return null;
    }
286451
public function get(string $name): ?string
    {
        $key = strtolower($name);
        if (!isset($this->headers[$key])) {
            return null;
        }

        return $this->headers[$key][1];
    }
642488
public function getHeaders($name = null)
    {
        if (is_null($name)) {
            return $this->headers;
        } else {
            return $this->getHeader($name);
        }
    }
170470
public function get(string $name)
    {
        if (!isset($this->_data[$name])) {
            return null;
        }

        return $this->_data[$name];
    }
283105
public function findHeaders($name)
    {
        return array_filter($this->getHeaders(), function ($header) use ($name) {
            return StringType::startsWith($header, "$name:");
        });
    }
520815
public function getValue($name)
    {
        $cookie = $this->get($name);

        return null === $cookie ? null : $cookie->getValue();
    }
421363
public function getHeader($name)
    {
        $name = mb_strtolower($name);
        return isset($this->headers[$name]) ? $this->headers[$name] : null;
    }
547880
public function getFirstTag($name)
    {
        foreach ($this->tags as $i => $tag) {
            if (strtolower($tag->getName()) == $name) {
                return $this->tags[$i];
            }
        }

        return null;
    }
686930
public function getLastHeader(string $name) : ?string
    {
        $name = strtolower($name);

        return isset($this->headers[$name]) ? end($this->headers[$name]) : null;
    }
1011670
public static function valueOf($name)
    {
        $names = static::getNames();
        return isset($names[$name]) ? $names[$name] : null;
    }