Currently the blob constructor creates a BLOB whose priv pointer is NULL when the encoding is the empty string:

new empty = blobcode.blob(encoded="");

An empty BLOB is a legitimate object, but priv==NULL does not play well with other VMODs expecting a BLOB.

The static null_blob, whose priv pointer points to the static constant empty string, was created for this purpose, and is returned by the decode function when the encoding is the empty string. The constructor should use it as well.