BUG #5560: pg_dump generates invalid DDL

The following bug has been logged online:

Bug reference: 5560
Logged by: Shigeru Hanada
Email address: hanada(at)metrosystems(dot)co(dot)jp
PostgreSQL version: 9.1devel
Operating system: Red Hat Enterprise Linux Server release 5.1 (Tikanga)
Description: pg_dump generates invalid DDL
Details:

When target database contains user mapping for public, pg_dump generates
invalid DDL with empty string like this.

CREATE USER MAPPING FOR "" SERVER srv;

This DDL causes error below.

ERROR: zero-length delimited identifier at or near """" at character 25
STATEMENT: CREATE USER MAPPING FOR "" SERVER srv;

How to reproduce:

psql<<EOF
CREATE FOREIGN DATA WRAPPER fdw;
CREATE SERVER srv FOREIGN DATA WRAPPER fdw;
CREATE USER MAPPING FOR PUBLIC SERVER srv;
EOF
pg_dump > mapping.sql
createdb newdb
psql -f mapping.sql newdb