Object reference not set to an instance of an object. appears when double click to select row from the gridView

I have 2 forms.. grid Form has a data Grid View gets its data from database, the second form other form has text boxes similar to the grid View Columns.

i want to select a row in the grid by double clicking and the other form must shown and the text boxes have the values from grid

Error Show

System.NullReferenceException

HResult=0x80004003

Message=Object reference not set to an instance of an object.

Source=HospitalDataStore StackTrace:

at HospitalDataStore.advSearchForm.dataGridView1_CellDoubleClick(Object sender, DataGridViewCellEventArgs e) in D:\Phoenix\px_software\px_projects\ICareProject\HospitalDataStore\HospitalDataStore\advSearchForm.cs:line 105 at System.Windows.Forms.DataGridView.OnCellDoubleClick(DataGridViewCellEventArgs e) at System.Windows.Forms.DataGridView.OnDoubleClick(EventArgs e)

Code is here

private void dataGridView1_CellDoubleClick(object sender,DataGridViewCellEventArgs e){


int rowIndex = e.RowIndex;
DataGridViewRow row = dataGridView1.Rows[rowIndex];
((InPatientForm)docInsForm).lblRegNo.Text = row.Cells[0].Value.ToString();
((InPatientForm)docInsForm).txtSearch.Text = row.Cells[1].Value.ToString();
 ((InPatientForm)docInsForm).lblName.Text = row.Cells[2].Value.ToString();
this.Close();
}