src/Viserio/Component/Http/AbstractMessage.php
public function getHeader($header): array
    {
        if (! $this->hasHeader($header)) {
            return [];
        }

        $header = \strtolower($header);
        $header = $this->headerNames[$header];
        $value  = $this->headers[$header];

        return \is_array($value) ? $value : [$value];
    }
public function getHeader($header): array
    {
        if (! $this->hasHeader($header)) {
            return [];
        }

        $header = \strtolower($header);
        $header = $this->headerNames[$header];
        $value  = $this->headers[$header];

        return \is_array($value) ? $value : [$value];
    }
{@inheritdoc}