X-Git-Url: http://nitlanguage.org

diff --git a/lib/core/collection/abstract_collection.nit b/lib/core/collection/abstract_collection.nit
index 5cffbec..04dabfa 100644
--- a/lib/core/collection/abstract_collection.nit
+++ b/lib/core/collection/abstract_collection.nit
@@ -385,7 +385,7 @@ end
 interface SimpleCollection[E]
 	super RemovableCollection[E]
 
-	# Add an item in a collection.
+	# Add `item` to this collection.
 	#
 	#     var a = [1,2]
 	#     a.add 3
@@ -457,7 +457,9 @@ interface Set[E]
 		var res = 23 + length
 		# Note: the order of the elements must not change the hash value.
 		# So, unlike usual hash functions, the accumulator is not combined with itself.
-		for e in self do res += e.hash
+		for e in self do
+			if e != null then res += e.hash
+		end
 		return res
 	end
 
@@ -857,6 +859,36 @@ interface SequenceRead[E]
 		end
 	end
 
+	# Try to get an element, return `null` if the `index` is invalid.
+	#
+	# ~~~
+	# var a = [10,20,30]
+	# assert a.get_or_null(1) == 20
+	# assert a.get_or_null(3) == null
+	# assert a.get_or_null(-1) == null
+	# assert a.get_or_null(-10) == null
+	# ~~~
+	fun get_or_null(index: Int): nullable E
+	do
+		if index >= 0 and index < length then return self[index]
+		return null
+	end
+
+	# Try to get an element, return `default` if the `index` is invalid.
+	#
+	# ~~~
+	# var a = [10,20,30]
+	# assert a.get_or_default(1, -1) == 20
+	# assert a.get_or_default(3, -1) == -1
+	# assert a.get_or_default(-1, -1) == -1
+	# assert a.get_or_default(-10, -1) == -1
+	# ~~~
+	fun get_or_default(index: Int, default: E): E
+	do
+		if index >= 0 and index < length then return self[index]
+		return default
+	end
+
 	# Get the last item.
 	# Is equivalent with `self[length-1]`.
 	#