`test` requires quotes around variables with =, or it can fail when the
variable is empty. In this case it would fail successfully (lol) but
print an ugly error message.
---
 src/cgi.fish | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/cgi.fish b/src/cgi.fish
index 1f66a18..721e7b3 100644
--- a/src/cgi.fish
+++ b/src/cgi.fish
@@ -41,7 +41,7 @@ end

 # check for file source mode
 set source_mode false
-if test $req_query = "source=1"
+if test "$req_query" = "source=1"
     set source_mode true
 end

--
2.35.1

I decided to apply this patch. As we discussed, it shouldn't be
necessary in theory, but there's no harm in adding the double quotes.
:)