[Gradle, JS] Make inputFileProperty optional

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/nodejs/NodeJsExec.kt

@@ -1,6 +1,6 @@
 /*
- * Copyright 2010-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
- * that can be found in the license/LICENSE.txt file.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlin.gradle.targets.js.nodejs
@@ -32,6 +32,7 @@ open class NodeJsExec : AbstractExecTask<NodeJsExec>(NodeJsExec::class.java), Re
     @Input
     var sourceMapStackTraces = true
 
+    @Optional
     @InputFile
     val inputFileProperty: RegularFileProperty = project.newFileProperty()