From https://ftp.gnu.org/gnu/bash/bash-5.0-patches/bash55-018

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

			     BASH PATCH REPORT
			     =================

Bash-Release:	5.0
Patch-ID:	bash50-018

Bug-Reported-by:	oguzismailuysal@gmail.com
Bug-Reference-ID:
Bug-Reference-URL:	https://lists.gnu.org/archive/html/bug-bash/2019-10/msg00098.html

Bug-Description:

In certain cases, bash does not perform quoted null removal on patterns
that are used as part of word expansions such as ${parameter##pattern}, so
empty patterns are treated as non-empty.

Patch (apply with `patch -p0'):

*** bash-5.0.17/subst.c	2020-04-02 17:14:58.000000000 -0400
--- b/subst.c	2020-07-09 15:28:19.000000000 -0400
***************
*** 5113,5116 ****
--- b/5113,5118 ----
  				      (int *)NULL, (int *)NULL)
  	     : (WORD_LIST *)0;
+   if (l)
+     word_list_remove_quoted_nulls (l);
    pat = string_list (l);
    dispose_words (l);

*** bash-5.0/patchlevel.h	2016-06-22 14:51:03.000000000 -0400
--- b/patchlevel.h	2016-10-01 11:01:28.000000000 -0400
***************
*** 26,30 ****
     looks for to find the patch level (for the sccs version string). */
  
! #define PATCHLEVEL 17
  
  #endif /* _PATCHLEVEL_H_ */
--- b/26,30 ----
     looks for to find the patch level (for the sccs version string). */
  
! #define PATCHLEVEL 18
  
  #endif /* _PATCHLEVEL_H_ */