Compiler error in TreePage's state.treeOrError.directories on IGitTree

Created by: JoshuaKGoldberg

After setting up a new repository locally following an install and build, directories is of type IGitTree | null[] in backend/graphqlschema.ts. The null[] seems... wrong? 😕

export interface IGitTree {
    __typename: 'GitTree'
    path: string
    isRoot: boolean
    name: string
    isDirectory: boolean
    commit: IGitCommit
    repository: IRepository
    url: string
    canonicalURL: string
    externalURLs: IExternalLink[]
    submodule: ISubmodule | null
    directories: IGitTree | null[]
    files: IFile[]
    entries: TreeEntry[]
    symbols: ISymbolConnection
    isSingleChild: boolean
}

TreePage.tsx is the only place where TypeScript complains:

this.state.treeOrError.directories.length
...
this.state.treeOrError.directories.map((e, i) => {
    ...
    name={e.name}
})

If the type is changed to IGitTree[], no more complaints.