Object reference not set to an instance of an object.

LabsResponse labresponse = new LabsResponse();
           Lab[] labs = new Lab[1];

           string cs = ConfigurationManager.ConnectionStrings["DatabaseContext"].ConnectionString;

           using (SqlConnection con = new SqlConnection(cs))
           {
               int i = 0;
               SqlCommand cmd = new SqlCommand("Select * from Labs where clinicNumber=" + clinicNumber, con);

               con.Open();
               SqlDataReader reader = cmd.ExecuteReader();

               while (reader.Read())
               {

                  labs[i].CategoryName =reader[0].ToString();
                 labresponse.Labs = labs;
                 i++;

               }
               con.Close();

               return labresponse;

  public partial class LabsResponse : ServiceResponse
    {

        private Lab[] labsField;

        /// <remarks />
        [System.Xml.Serialization.XmlArrayAttribute(IsNullable = true)]
        [System.Xml.Serialization.XmlArrayItemAttribute(Namespace = "http://schemas.datacontract.org/2004/07/Mayo.Cdans.Labs.Objects")]
        public Lab[] Labs
        {
            get
            {
                return this.labsField;
            }
            set
            {
                this.labsField = value;
            }
        }
    }

when i a trying to assign value to labs[i].CategoryName it gives above mentioned error what can be done please help. thanks in advance.