code: protected function findContentType($spaceId, $contentTypeName)
      {
          $contentTypes = $this->contentTypeRepo->findNewestByName($spaceId, $contentTypeName);
          if ($contentTypes->isEmpty()) {
              throw new InvalidArgumentException(
                  sprintf(
                      'Content type "%s" in space "%s" not found!',
                      $contentTypeName,
                      $spaceId
                  )
              );
          }
          if ($contentTypes->count() > 1) {
              throw new InvalidArgumentException(
                  sprintf(
                      'Multiple content types with name "%s" found in space "%s"!',
                      $contentTypeName,
                      $spaceId
                  )
              );
          }
          $contentType = $contentTypes->first();
          return $contentType;
      }
docs: Finds one content type by it's name.
  
  @param $spaceId
  @param $contentTypeName
  
  @return ContentfulContentType
  @throws InvalidArgumentException If a content type with the given name cannot be found.
  @throws InvalidArgumentException If multiple content type with the name are found.