Move to a note because it's a logical extension of the sentences

Author: benjie

spec/Section 6 -- Execution.md

@@ -922,14 +922,16 @@ that position is of a `Non-Null` type, then an execution error is raised at that
 position. The error must be added to the {"errors"} list in the _execution
 result_.
 
-Exactly one error must be added to the {"errors"} list for each {null} appearing
-in the _execution response_ because of an error (including error propagation).
 If a _response position_ resolves to {null} because of an execution error which
 has already been added to the {"errors"} list in the _execution result_, the
 {"errors"} list must not be further affected. If a sibling field of a response
 position that triggered error propagation also raises an error, this additional
 error must not be added to the {"errors"} list.
 
+Note: The result of the above is that exactly one error must be added to the
+{"errors"} list for each {null} appearing in the _execution response_ because of
+an error (including due to error propagation).
+
 Since `Non-Null` response positions cannot be {null}, execution errors are
 propagated to be handled by the parent _response position_. If the parent
 response position may be {null} then it resolves to {null}, otherwise if it is a