[BUG] invalid-null-argument outmem() src/output.c:149:17

Hello Dash maintainers,

I encountered a bug in Dash in commit b4ef25d7 and would like to report
it. The details are provided below.

output.c:149:25: runtime error: null pointer passed as argument 1, which 
is declared to never be null
/usr/include/string.h:402:14: note: nonnull attribute specified here
     #0 0x5f7d3a71f5d6 in outmem /upstream/ubsan/dash/src/output.c:149:17
     #1 0x5f7d3a720841 in doformat /upstream/ubsan/dash/src/output.c:343:2
     #2 0x5f7d3a7208f8 in out1fmt /upstream/ubsan/dash/src/output.c:275:2
     #3 0x5f7d3a721d96 in printfcmd 
/upstream/ubsan/dash/src/bltin/printf.c:232:5
     #4 0x5f7d3a6ddc85 in evalbltin /upstream/ubsan/dash/src/eval.c:975:12
     #5 0x5f7d3a6d8ef4 in evalcommand /upstream/ubsan/dash/src/eval.c:923:7
     #6 0x5f7d3a6d60ac in evaltree /upstream/ubsan/dash/src/eval.c:305:12
     #7 0x5f7d3a70218c in cmdloop /upstream/ubsan/dash/src/main.c:246:8
     #8 0x5f7d3a701e4b in main /upstream/ubsan/dash/src/main.c:180:3
     #9 0x724e14494249 in __libc_start_call_main 
csu/../sysdeps/nptl/libc_start_call_main.h:58:16
     #10 0x724e14494304 in __libc_start_main csu/../csu/libc-start.c:360:3
     #11 0x5f7d3a6a4930 in _start 
(/upstream/ubsan/dash/src/dash+0x42930) (BuildId: 
096851211111e4d689a2ea0deb5b5d647b8ebd40)

SUMMARY: UndefinedBehaviorSanitizer: invalid-null-argument output.c:149:25


Environment:

Debian-12, x86-64
clang-19 compiler

Steps to reproduce:

./autogen.sh
CC=clang CFLAGS=" -fsanitize=undefined -g " ./configure --disable-fnmatch
--disable-lineno --disable-glob
make
cd src
echo -e '""printf "%s"""' | ./dash