code: public function updateSetter($key, $value = null, $comment = null, $export = false)
      {
          $pattern = "/^(export\h)?\h*{$key}=.*/m";
          $line = $this->formatter->formatSetterLine($key, $value, $comment, $export);
          $this->buffer = preg_replace($pattern, $line, $this->buffer);
  
          return $this;
      }
docs: Update one setter in buffer
  
  @param  string       $key
  @param  string|null  $value
  @param  string|null  $comment
  @param  boolean      $export
  
  @return DotenvWriter