Why is prevState undefined?

Question

React

Here is my state

this.state = {
      location: null,
      latitude: null,
      longitude: null,
      carNum: {
        value: null,
        validPassenger: false,
        validTruck: false,
      },
      comment: {
        value: null,
        valid: false,
        validationRules: {
          minLength: 5
        }
      },
      coordinateTrigger: true,
      locationTrigger: true,
    };

Here is my input function

updateInputState = (key, value) => {
    this.setState(prevState => {
      return {
        [key]: {
          ...prevState[key],
          value: value,
          valid: validate(
            value,
            ...prevState[key]
          )
        }
      };
    });
  };

My input

<Textarea
  value={this.state.comment.value}
  onChangeText={val =>
    this.updateInputState("comment", val)
  }
/>

Tell me why it does not see prevState here?