Push PDF null when link destinations are missing values.
Push PDF null when link destinations are missing values.

Accidentally omitted in commit 4b2cb034c16708546ac4b5fbcb981949a4a12f5c

ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf