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='2021-05-22 23:39:27 +0200'>2021-05-22</span></td><td><a href='/guix/commit/tests/hackage.scm?id=cfec09a9928e171a724f630ba652ea0241d52e92'>import: hackage: Prefix licenses with 'license:'.</a><span class='msg-avail'>...</span></td><td>Xinglu Chen</td></tr>
<tr><td><span title='2019-06-20 14:07:01 +0200'>2019-06-20</span></td><td><a href='/guix/commit/tests/hackage.scm?id=b46a9b9a5e833989396565c9d924cc97ce080703'>import: hackage: Add two expected failing test cases.</a><span class='msg-avail'>...</span></td><td>Robert Vollmert</td></tr>
<tr><td><span title='2019-06-13 22:18:52 -0400'>2019-06-13</span></td><td><a href='/guix/commit/tests/hackage.scm?id=ca45da9fc9b1eee399ce4344b18cbb129daeca4c'>import: hackage: Handle Hackage revisions.</a><span class='msg-avail'>...</span></td><td>Robert Vollmert</td></tr>
<tr><td><span title='2019-06-02 22:16:05 +0200'>2019-06-02</span></td><td><a href='/guix/commit/tests/hackage.scm?id=959c9d159da2c53b87ae0af1421aecac98b20f46'>import: hackage: Parse braced properties.</a><span class='msg-avail'>...</span></td><td>Robert Vollmert</td></tr>
<tr><td><span title='2019-06-02 22:12:19 +0200'>2019-06-02</span></td><td><a href='/guix/commit/tests/hackage.scm?id=64d31813577b7471f819652e3ec81abb285bb77c'>tests: hackage: Test multiline cabal description.</a><span class='msg-avail'>...</span></td><td>Robert Vollmert</td></tr>
<tr><td><span title='2019-06-02 22:07:53 +0200'>2019-06-02</span></td><td><a href='/guix/commit/tests/hackage.scm?id=ea35f5c599a2fe4d6ab2925b1030f64e8b21e195'>tests: Fix hackage tests.</a><span class='msg-avail'>...</span></td><td>Robert Vollmert</td></tr>
<tr><td><span title='2019-06-01 15:26:30 +0200'>2019-06-01</span></td><td><a href='/guix/commit/tests/hackage.scm?id=0be465924c6f745618a73eea816aa15aba7c8d30'>tests: Indent hackage tests</a><span class='msg-avail'>...</span></td><td>Robert Vollmert</td></tr>
<tr><td><span title='2019-06-01 15:26:30 +0200'>2019-06-01</span></td><td><a href='/guix/commit/tests/hackage.scm?id=4110cde00560bd97cc8d83c34b80c52f37c680a2'>tests: hackage: Don't mock hackage-fetch.</a><span class='msg-avail'>...</span></td><td>Robert Vollmert</td></tr>
<tr><td><span title='2019-06-01 15:26:30 +0200'>2019-06-01</span></td><td><a href='/guix/commit/tests/hackage.scm?id=55c98f3261b6ced2c38e060566e1eb952bd3e42b'>tests: hackage: Factor out package pattern.</a><span class='msg-avail'>...</span></td><td>Robert Vollmert</td></tr>
<tr><td><span title='2019-05-26 23:20:30 +0200'>2019-05-26</span></td><td><a href='/guix/commit/tests/hackage.scm?id=ad7466aafd7f166d0b6be5eb32dda1d3ee8a6445'>import: hackage: Fix Cabal test.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>