@NotNull
  private List<FileReference> getFileReferences(@NotNull PyStringLiteralExpression expression) {
    final String value = expression.getStringValue();
    final Matcher matcher = DELIMITERS.matcher(value);
    int start = 0;
    int index = 0;
    final List<FileReference> results = new ArrayList<>();
    while (matcher.find()) {
      final String s = value.substring(start, matcher.start());
      if (!s.isEmpty()) {
        final TextRange range = TextRange.create(expression.valueOffsetToTextOffset(start),
                                                 expression.valueOffsetToTextOffset(matcher.start()));
        results.add(createFileReference(range, index++, s));
      }
      start = matcher.end();
    }
    final String s = value.substring(start);
    if (!s.isEmpty()) {
      final TextRange range = TextRange.create(expression.valueOffsetToTextOffset(start),
                                               expression.valueOffsetToTextOffset(value.length()));
      results.add(createFileReference(range, index, s));
    }
    return results;
  }
@NotNull
  private List<FileReference> getFileReferences(@NotNull PyStringLiteralExpression expression)