only the variable-length fields of a catalog tuple are permitted to be
NULL. For example, if you set pg_type.typrelid to be NULL, a
piece of code will likely perform "typetup->typrelid" (or, worse,
-"typetyp->typelem", which follows typrelid). This will result in
+"typetup->typelem", which follows typrelid). This will result in
random errors or even segmentation violations. Hence, do NOT insert
catalog tuples that contain NULL attributes except in their
variable-length portions! (The bootstrapping code is fairly good about