fix(stringify): reject invalid values in cast option objects

packages/csv-stringify/lib/api/index.js

@@ -161,12 +161,11 @@ const stringifier = function (options, state, info) {
             value !== undefined &&
             value !== null
           ) {
-            if (err)
-              return [
-                Error(
-                  `Invalid Casting Value: returned value must return a string, null or undefined, got ${JSON.stringify(value)}`,
-                ),
-              ];
+            return [
+              Error(
+                `Invalid Casting Value: returned value must return a string, null or undefined, got ${JSON.stringify(value)}`,
+              ),
+            ];
           }
           // Merge global options with the ones returned by cast
           options = { ...this.options, ...options };

packages/csv-stringify/test/option.cast.js

@@ -1,5 +1,6 @@
 import "should";
 import { stringify } from "../lib/index.js";
+import { stringify as stringifySync } from "../lib/sync.js";
 
 describe("Option `cast`", function () {
   describe("udf", function () {
@@ -22,6 +23,29 @@ describe("Option `cast`", function () {
   });
 
   describe("info object", function () {
+    for (const value of [0, false]) {
+      const message = `Invalid Casting Value: returned value must return a string, null or undefined, got ${JSON.stringify(value)}`;
+
+      it(`reject invalid value ${JSON.stringify(value)} in the callback API`, function (next) {
+        stringify(
+          [["input"]],
+          { cast: { string: () => ({ value }) } },
+          (err) => {
+            if (!err)
+              return next(Error("Expected an invalid casting value error"));
+            err.message.should.eql(message);
+            next();
+          },
+        );
+      });
+
+      it(`reject invalid value ${JSON.stringify(value)} in the sync API`, function () {
+        (function () {
+          stringifySync([["input"]], { cast: { string: () => ({ value }) } });
+        }).should.throw({ message });
+      });
+    }
+
     it("validate and normalize local options", function (next) {
       stringify(
         [["invalid cast"]],

packages/csv-stringify/test/option.cast.ts

@@ -195,6 +195,24 @@ describe("Option `cast`", function () {
   });
 
   describe("info object", function () {
+    it("accept string, null and undefined values in cast options", function (next) {
+      stringify(
+        [["empty", "null", "undefined", "text"]],
+        {
+          cast: {
+            string: (value, context) => ({
+              value: ["", null, undefined, "text"][context.index],
+            }),
+          },
+        },
+        (err, data) => {
+          if (err) return next(err);
+          data.should.eql(",,,text\n");
+          next();
+        },
+      );
+    });
+
     it("preserves a reused cast result", function (next) {
       const result = { value: "shared", quoted: true };
       stringify(