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EPUBCheck · Stylesheets

CSS-002

Updated:

EPUBCheck CSS-002 is an error message: “Empty or NULL reference found.” The CSS has an empty reference, such as url() with nothing inside.

The official message

Empty or NULL reference found.

Default severity
Error. The EPUB breaks a rule of the specification and is invalid. Stores and Send to Kindle may reject it, and EPUBCheck exits with status 1.
EPUBCheck version
5.4.0

Typical causes

  • A background or font URL removed without removing the declaration.

How to fix it

  • Delete the declaration or fill in the URL.

Terms used here

Other CSS messages

  • CSS-001 The "…" property must not be included in an EPUB Style Sheet.
  • CSS-003 CSS document is encoded in UTF-16. It should be encoded in UTF-8 instead.
  • CSS-004 CSS documents must be encoded in UTF-8, detected …;
  • CSS-006 CSS selector specifies fixed position.
  • CSS-007 Font-face reference "…" refers to non-standard font type "…".
  • CSS-008 An error occurred while parsing the CSS: ….

Message text and severity from EPUBCheck 5.4.0 (W3C, BSD-3-Clause). Explanation by EPUBLab.

FAQ

What does EPUBCheck CSS-002 mean?

EPUBCheck CSS-002 is an error message: “Empty or NULL reference found.” The CSS has an empty reference, such as url() with nothing inside.

Is CSS-002 an error?

CSS-002 is reported as error by default. The EPUB breaks a rule of the specification and is invalid. Stores and Send to Kindle may reject it, and EPUBCheck exits with status 1.