Error while assigning value to a map

[Vaibhav Kushwaha]

Hey there, I am trying to initialise a map Map<String, List<String> > mp with a value, I am attaching a code snippet below. However, it's giving me an error that the add() method was called on null object. Moreover, when I tried fixing it by using method 2, it gave me the error mentioned below it.

Approach 1:

values.forEach((item){

List<String> prop = item.split('/');

mp[prop[0]].add(prop[1]);

}

);

The above approach is giving me the null error so I tried this other approach.

Approach 2:

values.forEach((item){

List<String> prop = item.split('/');

final key = prop[0];

mp[key] = (mp[key] == null) ? List<String>():mp[key];

mp[key].add(prop[1]);

}

);

This approach gave me an error Unhandled Exception: RangeError (index): Invalid value: Only valid value is 0: 1

How do I resolve this error?

[Suzuki Tomohiro]

1. Learn how to use debugger. Add breakpoint at the problematic line to see why these exceptions occur.

2. Would you share some example for “values” variable?

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