Allow empty strings on replace pipe parameters (#66)

Author: fantoine

src/string/replace.pipe.ts

@@ -1,5 +1,5 @@
 import { Pipe, PipeTransform  } from '@angular/core';
-import { isString } from '../utils/utils';
+import { isString, isUndefined } from '../utils/utils';
 
 @Pipe({
   name: 'replace'
@@ -8,10 +8,10 @@ export class ReplacePipe implements PipeTransform {
 
   transform (input: any, pattern: any, replacement: any): any {
 
-    if (!isString(input) || !pattern || !replacement) {
+    if (!isString(input) || isUndefined(pattern) || isUndefined(replacement)) {
       return input;
     }
 
     return input.replace(pattern, replacement);
   }
-}
+}