how to initialize Empty array in stuct [Solidity]

I am suffering to initialize an empty array for struct when a struct is made.

pragma solidity ^0.5.1;
contract Board {
//storage
Post[] posts;

//struct
struct Post {
    address author;
    string title;
    string content;
    Comment[] comments;
}

struct Comment {
    address author;
    string comment;
}

//add-post
function addPost(address _author, string memory _title, string memory _content) public {
    posts.push(Post(_author, _title, _content, /* HERE IS THE PROBLEM POINT */));
}

}

I want to initialize the comments(struct member) with Empty Array(Type: Comment). Which code should I use for The Problem Point??

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