Vue warns me Cannot set reactive property on undefined, null, or primitive value: null

Question

While fetching data from Firebase I am trying to set the properties of the object obtained to the UI, but when I try and set any changes to the data, it throws me this error.
Error in v-on handler: "TypeError: Cannot use 'in' operator to search for 'cc' in null.

I am using Vue in development mode, along with Firebase.Is there any concept I am missing out on?

beforeCreate(){
sref.get().then(sc => {
      if (sc.exists) {
        console.log(sc.data()); //this logs in the correct data
        this.school = sc.data(); //this too
        this.cc = sc.data().cc;  //also this
        this.name = sc.data().name;

When I do

console.log(this.name)

In created() it displays undefined, any attempt to change or update also gives an error

Vue warn]: Cannot set reactive property on undefined, null, or primitive value: null
[Vue warn]: Error in v-on handler: "TypeError: Cannot use 'in' operator to search for 'cc' in null"

found in

---> <VSelect>
       <VForm>
         <VCard>

TypeError: Cannot use 'in' operator to search for 'cc' in null
    at Proxy.set 

Answer 1

I had the same error attempting to set data in the v-model. My setup was as follows:

<template>
      <v-text-field
        v-model="this.myVariable"
        :readonly="false"
        :disabled="false"
        persistent-hint
        outlined
      ></v-text-field>
</template>

data() {
    return {
      myVariable: "1",
    }
}

This was not updating myVariable because of the this keyword on the line setting the v-model. Changing to the following resolved the errors for me:

<template>
      <v-text-field
        v-model="myVariable"
        :readonly="false"
        :disabled="false"
        persistent-hint
        outlined
      ></v-text-field>
</template>

data() {
    return {
      myVariable: "1",
    }
}

Answer 2

I figured out where I went wrong there, in my template v-model i was using this.school, this.name, this.cc which was causing the warnings to come, but I am still not clear at the internals of the working. I would like if someone pointed me to the right resources.