Compilation error cannot invoke method toInteger on null object

[cryptax]

The project wouldn't compile in my case. I was getting the error " Cannot invoke method toInteger() on null object" on the minSdkVersion line of app/build.gradle. I had to do the following quick fix:

    defaultConfig {
         // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
         applicationId "com.johnnysbug.flutterdle"
-        minSdkVersion localProperties.getProperty('flutter.minSdkVersion').toInteger()
+        minSdkVersion 16
         targetSdkVersion flutter.targetSdkVersion
         versionCode flutterVersionCode.toInteger()
         versionName flutterVersionName