Fix string.find (#1390)

common/space_lua/stdlib/string.ts

@@ -94,7 +94,7 @@ export const stringApi = new LuaTable({
         const reg = new RegExp(pattern);
         const index = s.slice(init - 1).search(reg);
 
-        if (index < 0) return;
+        if (index < 0) return null;
 
         const match = s.slice(init - 1).match(reg);
         const result = [index + init, index + init + match![0].length - 1];

common/space_lua/stdlib/string_test.lua

@@ -185,3 +185,9 @@ assertEqual(#matches, 3)
 assertEqual(matches[1][1], "ll")
 assertEqual(matches[2][1], "lll")
 assertEqual(matches[3][1], "l")
+
+-- https://community.silverbullet.md/t/test-if-string-find-outputs-nil-not-working-as-expected/2342
+assert(string.find("a", "b") == nil)
+assert(not (string.find("a", "b") ~= nil))
+assert(string.match("a", "b") == nil)
+assert(not (string.match("a", "b") ~= nil))