src/ThemeManager/ThemeCollection.php
public function themeExists($name)
    {
        return in_array($name, $this->themeNames) && ! is_null($this->getTheme($name));
    }
public function themeExists($name)
    {
        return in_array($name, $this->themeNames) && ! is_null($this->getTheme($name));
    }
@param $name

@return bool