if(array == null || array.Length == 0)
datatype[] arr = new datatype[]{};
or
datatype[] arr = new datatype[0];
or
datatype[] array = {}
or
var a = Array.Empty<datatype>();
object[] emptyArray = new object[0];
var listOfStrings = new List<string>();
// do stuff...
string[] arrayOfStrings = listOfStrings.ToArray();