[fix] flatten arrays when normalizing for serialization

Author: line-o

exist-core/src/main/java/org/exist/xquery/functions/fn/FunSerialize.java

@@ -28,6 +28,7 @@
 import org.exist.storage.serializers.EXistOutputKeys;
 import org.exist.util.serializer.XQuerySerializer;
 import org.exist.xquery.*;
+import org.exist.xquery.functions.array.ArrayType;
 import org.exist.xquery.functions.map.AbstractMapType;
 import org.exist.xquery.util.SerializerUtils;
 import org.exist.xquery.value.*;
@@ -157,6 +158,12 @@ public static Sequence normalize(final Expression callingExpr, final XQueryConte
                         "It is an error if an item in the sequence to serialize is an attribute node or a namespace node.");
                 }
                 temp.add(next);
+            } else if (itemType == Type.ARRAY) {
+                 final Sequence sequence = ArrayType.flatten(next);
+                 if (sequence.isEmpty()) {
+                     continue;
+                 }
+                 temp.add(new StringValue(callingExpr, sequence.getStringValue()));
             } else {
                 // atomic value
                 // "For each item in S1, if the item is atomic, obtain the lexical representation of the item by

exist-core/src/test/xquery/xquery3/serialize.xql

@@ -989,7 +989,7 @@ function ser:array-with-members-serializes-to-empty-string() {
 };
 
 declare
-    %test:assertEquals("|")
+    %test:assertEquals("")
 function ser:sequence-of-empty-arrays-serializes-to-empty-string() {
     serialize(([],[]), map{"item-separator": "|"})
 };