Gatsby 테마 바꾸기

Cannot read properties of null (reading 'split')

  31 |
  32 |   edges.forEach(({ node }) => {
> 33 |     const postCategories = node.frontmatter.categories.split(' ');
     |                                                        ^
  34 |     postCategories.forEach((category) => categorySet.add(category));
  35 |   });
  36 |

File: gatsby-node.js:33:56