NavController navigate doesn't work when I put a non-null value to a nullable List field of it's parameter

Question

I have a destination that accepts a model that have a nullable field. Before, because that nullable field isn't that important (as I have other ways to get the value of that nullable field, basically the nullable field is many-to-many relationship), I didn't bother to get that field's value on my API. But now that I have time to optimize my processes, I finally fixed my API and now I'm also passing the value of the m2m field. But, for some reason, having that value breaks the NavController's navigate(), which was previously ok with a null value for that m2m field. Both models are already Serializable. This is the error I'm getting:

The fragment SomeFragment is unknown to the FragmentNavigator. Please use the navigate() function to add fragments to the FragmentNavigator managed FragmentManager

My models looks like this:

data class Account(
    @SerializedName("id") var id: String,
    ... some other fields
    @SerializedName("m2m_field") var model1s: List<Model1>?,
) : java.io.Serializable

//Model1 seems to not need @SerializedName(), and I can use it for other Retrofit calls without any issue
//I even got an error when I added @SerializedName() to the fields
data class Model1(
    @PrimaryKey(autoGenerate = false) @ColumnInfo(name = "id") var id: String,
    @ColumnInfo(name = "created_at") var created_at: String,
    ... some other fields
) : java.io.Serializable

Answer 1

I already found the answer to this. The cause was kinda silly, the reason was that I have a field on Model1 that is alright to get null on my use-case, but I didn't declare it as nullable. And something doesn't like that. So check carefully your Retrofit response and it's corresponding model and make sure that they are 100% compatible.