Native crash when using an undefined Animated.Value in a debug node

When setting the value of an Animated.Value object to null or undefined and then using it in a debug statement in an Animated.Code block, we get a native exception that crashes the app.

Reproducible demo:

import React, {Fragment} from 'react';
import {
  SafeAreaView,
  Text,
  TouchableOpacity,
} from 'react-native';

import Animated from 'react-native-reanimated';
const {
  set,
  block,
  debug,
} = Animated;

const node = new Animated.Value(0);

const App = () => {
  return (
    <Fragment>
      <Animated.Code>
        {() => block([debug('node value: ', node)])}
      </Animated.Code>
      <SafeAreaView>
        <TouchableOpacity
          onPress={() => node.setValue(undefined)}    // setValue(null) will throw a different exception
          style={{padding: 20}}
        >
          <Text>Click Me</Text>
        </TouchableOpacity>
      </SafeAreaView>
    </Fragment>
  );
};

export default App;

This error can be quite difficult to find in a complex animation, since there is no indication about what the problem is. If it is intended that an error is thrown on an undefined Value, then a better error message would be very useful.

The exact error is on line 21 of REAJSCallNode.m:

[error][tid:main][RCTUIManager.m:1133] Exception thrown while executing UI block: *** -[__NSArrayM setObject:atIndexedSubscript:]: object cannot be nil

In the case of setting the Value to null, we get a JS exception: Unhandled JS Exception: Cannot read property '__isProxy' of null.

Here are the versions used:

"react": "16.8.6",
"react-native": "0.60.5",
"react-native-reanimated": "1.2.0"

[Sevendaye]

this.position = new Animated.ValueXY();

… onPanResponderMove: (event, gesture) => { this.position.setValue({ x: gesture.dx, y: 0}) }, …

Even if you only use x, you must put y to 0 so that they are not undefined It should have default values if not initialized.

[jakub-gonet]

@marqroldan, could you please provide some minimal code example reproducing this crash?