Add one additioanl example. update nav

Author: mnd999

modules/ROOT/pages/errors/gql-errors/22NC2.adoc

@@ -1,7 +1,7 @@
 = 22NC2
 
 == Status description
-error: data exception - node element type is ineffectual. The node element type `{ <<label>> }` must contain one or more implied labels, or define at least one property type.
+error: data exception - node element type is ineffectual. The node element type `{ <<label>> }` must contain one or more implied labels, or at least one property type.
 
 == Explanation
 When defining a graph type, node element types have some effect.
@@ -21,7 +21,7 @@ An error will be thrown with GQLSTATUS 22NC2 and the status description:
 
 [source]
 ----
-error: data exception - node element type is ineffectual. The node element type `Node` must contain one or more implied labels, or define at least one property type.
+error: data exception - node element type is ineffectual. The node element type `Node` must contain one or more implied labels, or at least one property type.
 ----
 
 This can be corrected by defining at least one property type or by adding an implied label e.g.:

modules/ROOT/pages/errors/gql-errors/22NC5.adoc

@@ -58,9 +58,32 @@ In this case, the reference could be corrected by providing a relationship type:
 ALTER CURRENT GRAPH TYPE SET {
   CONSTRAINT FOR ()-[b:REL]->() REQUIRE (b.prop) IS KEY
 }
+----
+
+=== Element reference ommitted from constraint definition ===
+In this example, a constraint is defined with an empty node element type reference, which is not allowed: 
 
+[source,cypher]
+----
+ALTER CURRENT GRAPH TYPE SET {
+    CONSTRAINT FOR () REQUIRE n.prop IS UNIQUE
 ----
 
+An error will be thrown with GQLSTATUS 22NC5 and the status description:
+
+[source]
+----
+error: data exception - graph type element not found. The node type element referenced by 'n' was not found.
+----
+In this case, the reference can be corrected by providing a Label for the constraint:
+
+[source,cypher]
+----
+ALTER CURRENT GRAPH TYPE SET {
+    CONSTRAINT FOR (n:Node) REQUIRE n.prop IS UNIQUE
+----
+
+
 ifndef::backend-pdf[]
 [discrete.glossary]
 == Glossary

modules/ROOT/pages/errors/gql-errors/22NC8.adoc

@@ -1,4 +1,4 @@
-= 22NC9
+= 22NC8
 
 == Status description
 error: data exception - graph type contains duplicated tokens. The graph type includes a label, relationship type or alias with name `{ <<token>> }` more than once

modules/ROOT/pages/errors/gql-errors/22NC9.adoc

@@ -1,4 +1,4 @@
-= 22NCA
+= 22NC9
 
 == Status description
 error: data exception - invalid element type constraints in graph type. A `{ <<entityType>> }` element type property `{ <<context>> }` constraint cannot be specified inline of a `{ <<entityType2>> }` element type