Error when string.split is given empty separator (#13132)

builtin/common/misc_helpers.lua

@@ -170,6 +170,9 @@ end
 --------------------------------------------------------------------------------
 function string.split(str, delim, include_empty, max_splits, sep_is_pattern)
 	delim = delim or ","
+	if delim == "" then
+		error("string.split separator is empty", 2)
+	end
 	max_splits = max_splits or -2
 	local items = {}
 	local pos, len = 1, #str

builtin/common/tests/misc_helpers_spec.lua

@@ -38,6 +38,12 @@ describe("string", function()
 			assert.same({ "one", "two" }, string.split("one,two", ",", false, -1, true))
 			assert.same({ "one", "two", "three" }, string.split("one2two3three", "%d", false, -1, true))
 		end)
+
+		it("rejects empty separator", function()
+			assert.has.errors(function()
+				string.split("", "")
+			end)
+		end)
 	end)
 end)