AV1553: Updated text to match with AV1135 (#255)

Author: bkoelman

_rules/1553.md

@@ -12,7 +12,7 @@ The only valid reason for using C# 4.0's optional parameters is to replace the e
 		return someText.IndexOf(phrase, startIndex, length);
 	}
 
-Since strings, lists and collections should never be `null` according to rule [{{ site.default_rule_prefix }}1135](/member-design-guidelines#{{ site.default_rule_prefix }}1135), if you have an optional parameter of these types with default value `null` then you must use overloaded methods instead.
+Since strings, collections and tasks should never be `null` according to rule [{{ site.default_rule_prefix }}1135](/member-design-guidelines#{{ site.default_rule_prefix }}1135), if you have an optional parameter of these types with default value `null` then you must use overloaded methods instead.
 
 Strings, unlike other reference types, can have non-null default values. So an optional string parameter may be used to replace overloads with the condition of having a non-null default value.