error[E0277]: the trait bound `NotesDs: Serialize` is not satisfied

Question

#[derive(BorshSerialize, BorshDeserialize)]
pub struct NotesDs {
    pub own: Vec<String>,
    pub shared: UnorderedMap<AccountId,Vec<String>>,
}

impl NotesDs{
    pub fn new() -> Self {
        assert!(env::state_read::<Self>().is_none(), "Already initialized");
        Self {
            own: Vec:: new(),
            shared: UnorderedMap::new(b"w".to_vec()),
        }
    }
}
#[near_bindgen]
#[derive(BorshDeserialize, BorshSerialize)]
pub struct Note {
    pub note_list : UnorderedMap<AccountId,NotesDs>, 
}

impl Default for Note {
    fn default() -> Self {
        // Check incase the contract is not initialized
        env::panic(b"The contract is not initialized.")
    }
}

#[near_bindgen]
impl Note {
    /// Init attribute used for instantiation.
    #[init]
    pub fn new() -> Self {
        assert!(env::state_read::<Self>().is_none(), "Already initialized");
        Self {
            note_list: UnorderedMap::new(b"h".to_vec()),
        }
    }
    pub fn get_note_list(&mut self, account_id: AccountId) -> NotesDs {
        self.note_list.get(&account_id).unwrap()
    }
}

Problem Defination

This causes an error
error[E0277]: the trait bound NotesDs: Serialize is not satisfied
#[near_bindgen] - the trait Serialize is not implemented for 'NotesDs'
note: required because of the requirements on the impl of Serialize for Vec<NotesDs> note: required by a bound in to_vec

Cargo.toml

[package]
name = "test101"
version = "0.1.0"
edition = "2021"

[lib]
crate-type = ["cdylib", "rlib"]

[dependencies]
near-sdk = "3.1.0"
serde_json = "1.0.2"

[profile.release]
codegen-units = 1
opt-level = "z"         
lto = true              
debug = false          
panic = "abort"         
overflow-checks = true  

I tried adding Serialize and Deserialize to all of my structs and enums.

The main problem is coming when the return value is of the type NotesDs, the functions where it is not the return type are working fine.

I even tried initializing the custom defined struct in a separate file and importing it. But I still get the error.