[C#] nullreferenceexception when searching in datagridview from another form

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C#

Visual-Studio

optimization

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I do not know what is causing this problem. I have 2 forms (Search form & Accounts form) in Accounts Form there is a Search button which opens the Search.
Code for opening the search form:

private void btnSearch_Click(object sender, EventArgs e) {
            SearchForm sf = new SearchForm();
            sf.ShowDialog();
        }

In the search form, these are the codes:

public partial class SearchForm : Form {
        public static string search;
        private readonly AcctsForm rf;

        public SearchForm(AcctsForm actform) {
            rf = actform;
        }

        public SearchForm() {
            InitializeComponent();
        }

        private void btnOK_Click(object sender, System.EventArgs e) {
            search = textBox1.Text;
            rf.SearchedList("SELECT * FROM Employees_Info WHERE Emp_ID = @Search");
            this.Close();
        }
    }

From Accounts Form (The SearchedList event is referenced by the Search OK button):

public void SearchedList(string x) {
            try {
                using (sqlSelect = new SqlDataAdapter(x, conn)) {
                    sqlSelect.SelectCommand.Parameters.AddWithValue("@Search", SearchForm.search);
                    sqldt = new DataTable();
                    sqlSelect.Fill(sqldt);
                    if (sqldt.Rows.Count >= 1) {
                        dgvEmployees.DataSource = sqldt;
                    } else {
                        MessageBox.Show("not results found.");
                    }
                }
            } catch (SqlException err) {
                MessageBox.Show(err.Message);
            } finally {
                if (conn.State == ConnectionState.Open) {
                    conn.Close();
                }
            }
        }

What I have tried:

When I search a value/data in the search textbox that is not registered in the database, the "no results found" messagebox works, but when correct a correct one is inputted it will give a NullReferenceException. I already googled everything and tried "instantiating" the Accounts Forum but it doesn't do anything (Modifiers are already set to Public). Any ideas? Thank you in advance whoever can help!