How is it possible to Lerp from a non initialized value to an initialized value?

Question

I am confused how I can Lerp from inputDirection to targetInput when inputDirection has not yet been initialized, only defined. This piece of code is from a tutorial and I know it works, but I don't know why. My guess is that inputDirection is a special type of Vector3 that is a reference to user input or that the default value for Vector3 is (0, 0, 0), but my research so far has been unsuccessful.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.InputSystem;
 
 public class PlayerMovement : MonoBehaviour
 {
  private PlayerInputActions inputActions;
  private Vector2 movementInput;
  [SerializeField]
  private float moveSpeed = 10f;
  private Vector3 inputDirection;
  private Vector3 moveVector;
  private Quaternion currentRotation;
  void Awake()
  {
   inputActions = new PlayerInputActions();
   inputActions.Player.Movement.performed += context => movementInput = context.ReadValue<Vector2>();
   //Reads a Vector2 value from the action callback, stores it in the movementInput variable, and adds movementInput to the performed action event of the player
  }
  void FixedUpdate()
  {
   float h = movementInput.x;
   float v = movementInput.y;
 
   //y value in the middle
   //0 since no jump
   Vector3 targetInput = new Vector3(h, 0, v);
   inputDirection = Vector3.Lerp(inputDirection, targetInput, Time.deltaTime * 10f);
  }
 }

Answer 1

Vector3 is a struct (not a class) which means that all the fields inside of it are initialized with their default values. That's why it is (0, 0, 0) if you don't initialize by yourself with other value (because the default value of float, which is the type of x, y and z, is 0).