Cannot set non-nullable LiveData value to null

Question

The error from the title is returned for the following code, which makes no sense

private val _error = MutableLiveData<String?>()
val error: LiveData<String?> get() = _error


_error.postValue(null)  //Error Cannot set non-nullable LiveData value to null [NullSafeMutableLiveData]

parameter String of _error is obviously nullable, am I doing something wrong?

Answer 1

This appears to be related to a bug already reported against androidx.lifecycle pre-release of 2.3.0 https://issuetracker.google.com/issues/169249668.

Workarounds I have found:

1. turn off or reduce severity of NullSafeMutableLiveData in

build.gradle

android {
  ...
  lintOptions {
    disable 'NullSafeMutableLiveData'
  }
}

or lint.xml in root dir

<?xml version="1.0" encoding="UTF-8"?>
<lint>
    <issue id="NullSafeMutableLiveData" severity="warning" />
</lint>

2. Do the work for MutableLiveData encapsulation via backing properties dance (which really hurts my eyes).

class ExampleViewModel : ViewModel() {

    private val _data1 = MutableLiveData<Int>()
    val data1: LiveData<Int> = _data1

    private val _data2 = MutableLiveData<Int?>()
    val data2: LiveData<Int?> = _data2

    fun funct() {
        _data1.value = 1
        _data2.value = null
    }
}