Don't change behavior for Kerns.

mpetroff · mpetroff · commit f5907f3b020d · 2020-07-12T17:45:03.000Z
diff --git a/lib/matplotlib/mathtext.py b/lib/matplotlib/mathtext.py
@@ -2888,8 +2888,10 @@ def operatorname(self, s, loc, toks):
                 c.font = 'rm'
                 c._update_metrics()
                 hlist_list.append(c)
-            else:
+            elif isinstance(c, str):
                 hlist_list.append(Char(c, state))
+            else:
+                hlist_list.append(c)
         next_char_loc = loc + len(toks[0]) + 1
         if isinstance(toks[0], ParseResults):
             next_char_loc += 14  # Skip `operatorname{}`
