Fix contributed upstream here:
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=42694.

Index: emacs-26.3/src/xfns.c
===================================================================
--- emacs-26.3.orig/src/xfns.c
+++ emacs-26.3/src/xfns.c
@@ -2628,6 +2628,8 @@ xic_free_xfontset (struct frame *f)
 static XIMStyle
 best_xim_style (XIMStyles *xim)
 {
+  if (xim == NULL) goto out;
+
   int i, j;
   int nr_supported = ARRAYELTS (supported_xim_styles);

@@ -2636,6 +2638,7 @@ best_xim_style (XIMStyles *xim)
       if (supported_xim_styles[i] == xim->supported_styles[j])
	return supported_xim_styles[i];

+ out:
   /* Return the default style.  */
   return XIMPreeditNothing | XIMStatusNothing;
 }
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<tr><td><span title='2021-05-04 11:52:23 +0200'>2021-05-04</span></td><td><a href='/guix/commit/etc/committer.scm.in?id=570b3d32b92fb2220c5ecd9302f4fa85947d4bff'>etc: Break long lines in commit messages.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2021-04-12 21:42:15 +0200'>2021-04-12</span></td><td><a href='/guix/commit/etc/committer.scm.in?id=a6ac141ebb2efabbd47cbb04dfeb13779b7e50f6'>etc/committer: Add missing newline.</a><span class='msg-avail'>...</span></td><td>Morgan Smith</td></tr>
<tr><td><span title='2021-04-12 21:42:15 +0200'>2021-04-12</span></td><td><a href='/guix/commit/etc/committer.scm.in?id=d375eddda0b407b29ce0f7d29a582623cef20a89'>etc/committer: Use git plumbing instead of porcelain.</a><span class='msg-avail'>...</span></td><td>Morgan Smith</td></tr>
<tr><td><span title='2021-04-08 17:12:06 +0200'>2021-04-08</span></td><td><a href='/guix/commit/etc/committer.scm.in?id=c762df54786fd6f005f3b5307323f1d2df3cbf0b'>etc/committer: Disable diff colors.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2021-04-08 03:10:14 +0200'>2021-04-08</span></td><td><a href='/guix/commit/etc/committer.scm.in?id=83991a34d5c1d4985e54dd029a81412277ad062a'>etc/committer: Recompute hunks before processing changes.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2021-04-08 03:10:14 +0200'>2021-04-08</span></td><td><a href='/guix/commit/etc/committer.scm.in?id=43fb6b765d82ea5acfdc83f61472d99594ee1cbf'>etc/committer: Record minimal context for hunks to avoid problems.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2021-04-08 03:10:14 +0200'>2021-04-08</span></td><td><a href='/guix/commit/etc/committer.scm.in?id=56270c1275d8dcdec80c04c032079b694204052a'>etc/committer: Define delay duration as a variable.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2021-04-08 03:10:13 +0200'>2021-04-08</span></td><td><a href='/guix/commit/etc/committer.scm.in?id=c8c3afe8485bd614692f13e1e8a4200136da1302'>etc/committer: Handle package additions.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
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