fix: map filter allow nil results in strict mode, fixes #647

src/template/filter.spec.ts

@@ -31,7 +31,10 @@ describe('filter', function () {
   it('should render a simple filter', async function () {
     expect(await toPromise(new Filter('upcase', (x: string) => x.toUpperCase(), [], liquid).render('foo', ctx))).toBe('FOO')
   })
-
+  it('should reject promise when filter throws', async function () {
+    const filter = new Filter('foo', function * () { throw new Error('intended') }, [], liquid)
+    expect(toPromise(filter.render('foo', ctx))).rejects.toMatch('intended')
+  })
   it('should render filters with argument', async function () {
     const two = new NumberToken('2', 0, 1, undefined)
     expect(await toPromise(new Filter('add', (a: number, b: number) => a + b, [two], liquid).render(3, ctx))).toBe(5)

src/template/filter.ts

@@ -27,6 +27,6 @@ export class Filter {
       if (isKeyValuePair(arg)) argv.push([arg[0], yield evalToken(arg[1], context)])
       else argv.push(yield evalToken(arg, context))
     }
-    return this.handler.apply({ context, liquid: this.liquid }, [value, ...argv])
+    return yield this.handler.apply({ context, liquid: this.liquid }, [value, ...argv])
   }
 }