message: Prefer undefined rather than null
diff: @@ -29,7 +29,7 @@ interface Content {
  * The dirty (under editing) content of the LaTeX file if opened in vscode,
  * the content on disk otherwise.
  */
  - content: string | null,
  + content: string | undefined,
  /**
  * Completion item and other items for the LaTeX file.
  */
  @@ -135,7 +135,7 @@ export class Manager {
  private invalidateCachedContent(filePath: string) {
  if (filePath in this.cachedContent) {
  - this.cachedContent[filePath].content = null
  + this.cachedContent[filePath].content = undefined
  }
  }
  