Update explanation for predicate functions when used with null values

modules/ROOT/pages/functions/predicate.adoc

@@ -41,7 +41,8 @@ CREATE
 == all()
 
 The function `all()` returns `true` if the predicate holds for all elements in the given list.
-`null` is returned if the list is `null` or all of its elements are `null`.
+
+`null` is returned if the list is `null` or if the predicate evaluates to `null` for at least one element and does not evaluate to `false` for any other element.
 
 *Syntax:*
 
@@ -113,7 +114,8 @@ All nodes in the returned paths will have a property `age` with a value larger t
 == any()
 
 The function `any()` returns `true` if the predicate holds for at least one element in the given list.
-`null` is returned if the list is `null` or all of its elements are `null`.
+
+`null` is returned if the list is `null`, or if the predicate evaluates to `null` for at least one element and does not evaluate to `true` for any other element.
 
 *Syntax:*
 
@@ -429,7 +431,8 @@ Thus, `isEmpty()` is not suited to test for `null`-values.
 == none()
 
 The function `none()` returns `true` if the predicate does _not_ hold for any element in the given list.
-`null` is returned if the list is `null` or all of its elements are `null`.
+
+`null` is returned if the list is `null`, or if the predicate evaluates to `null` for at least one element and does not evaluate to `true` for any other element.
 
 *Syntax:*
 
@@ -499,7 +502,8 @@ No node in the returned paths has a property `age` with the value `25`.
 == single()
 
 The function `single()` returns `true` if the predicate holds for exactly _one_ of the elements in the given list.
-`null` is returned if the list is `null` or all of its elements are `null`.
+
+`null` is returned if the list is `null`, or if the predicate evaluates to `null` for at least one element and `true` for max one element.
 
 *Syntax:*
 
@@ -558,4 +562,3 @@ In every returned path there is exactly one node that has a property `eyes` with
 |===
 
 ======
-