code: protected function normalizeHeaderName($keyName)
      {
          if (!is_string($keyName)) {
              return null;
          }
  
          return ucwords(trim(strtolower($keyName)), '-') ?: null;
      }
docs: Normalize Real Header Name
  
  @param string $keyName Header Name key, The key will be convert into
  First Character after `-`(dash) into uppercase
  And space will be replace as `dash`
  @return null|string