null is not an object (evaluating ‘user.uid’)

I want to retrieve a field value of a document in Users collection by referencing it via the where condition from Firestore. I use the context api to pass the user object of the logged in user in my app. I get this error that user.uid is null. I can’t spot where the mistake is. I have added the relevant piece of code.

EditProfile.js

const EditProfile = () => {
  const { user } = React.useContext(AuthContext);

  const [name, setName] = React.useState();

  React.useEffect(() => {
    const userid = user.uid;
    const name = getFieldValue("Users", userid);
    setName(name);
  }, []);

  
};

export default EditProfile;

passing and getting value via context

export const AuthContext = React.createContext();

export const AuthProvider = ({ children }) => {
  const [user, setUser] = React.useState(null);

  return (
    <AuthContext.Provider
      value={{
        user,
        setUser,
      }}
    >
      {children}
    </AuthContext.Provider>
  );
};

const AppStack = () => {
  return (
    <AuthProvider>
      <BottomTab.Navigator>
        <BottomTab.Screen
          name="ProfileStack"
          component={ProfileStack}
        />
      </BottomTab.Navigator>
    </AuthProvider>
  );
};

export default AppStack;

ProfileStack.js

export const ProfileStack = ({ navigation }) => {
  return (
    <Stack.Navigator>
      <Stack.Screen
        name="Profile"
        component={Profile}
      />
      <Stack.Screen
        name="EditProfile"
        component={EditProfile}
      />
    </Stack.Navigator>
  );
};

getFieldValue function

export const getFieldValue = (collection, userid) => {
    firestore()
      .collection(collection)
      .where("userid", "==", userid)
      .get()
      .then((querySnapshot) => {
        if (querySnapshot.size === 0) {
          return "";
        }
        if (querySnapshot.size === 1) {
          const { name } = querySnapshot[0].data();
          return name;
        }
      })
      .catch((e) => console.log(e));
  };