fix: handle undefined replacement argument in replace filter (#864)

src/filters/string.ts

@@ -137,6 +137,7 @@ export function capitalize (this: FilterImpl, str: string) {
 export function replace (this: FilterImpl, v: string, pattern: string, replacement: string) {
   const str = stringify(v)
   pattern = stringify(pattern)
+  replacement = stringify(replacement)
   this.context.memoryLimit.use(str.length + pattern.length + replacement.length)
   return str.split(pattern).join(replacement)
 }

test/integration/filters/string.spec.ts

@@ -109,6 +109,14 @@ describe('filters/string', function () {
     return test('{{ "Take my protein pills and put my helmet on" | replace: "my", "your" }}',
       'Take your protein pills and put your helmet on')
   })
+  it('should support replace with undefined replacement', function () {
+    return test('{{ "Take my protein pills and put my helmet on" | replace: "my" }}',
+      'Take  protein pills and put  helmet on')
+  })
+  it('should support replace with undefined variable as replacement', function () {
+    return test('{{ "Take my protein pills and put my helmet on" | replace: "my", missing_variable }}',
+      'Take  protein pills and put  helmet on')
+  })
   it('should support replace_first', function () {
     return test('{% assign my_string = "Take my protein pills and put my helmet on" %}\n' +
             '{{ my_string | replace_first: "my", "your" }}',