public @NotNull Document getDocument() {
      Document document = FileDocumentManager.getInstance().getDocument(virtualFile, project);
      if (document == null) {
        Language language = (virtualFile instanceof LightVirtualFile) ? ((LightVirtualFile)virtualFile).getLanguage() : null;
        throw new AssertionError(String.format("no document for: %s (fileType: %s, language: %s, length: %s, valid: %s)",
                                               virtualFile,
                                               virtualFile.getFileType(), language, virtualFile.getLength(), virtualFile.isValid()));
      }
      return document;
    }
public @NotNull Document getDocument()