Fix empty xml tag handling for Set shapes (#973)

Author: kstich

codegen/smithy-aws-typescript-codegen/src/main/java/software/amazon/smithy/aws/typescript/codegen/XmlShapeDeserVisitor.java

@@ -24,8 +24,10 @@
 import software.amazon.smithy.model.Model;
 import software.amazon.smithy.model.shapes.CollectionShape;
 import software.amazon.smithy.model.shapes.DocumentShape;
+import software.amazon.smithy.model.shapes.ListShape;
 import software.amazon.smithy.model.shapes.MapShape;
 import software.amazon.smithy.model.shapes.MemberShape;
+import software.amazon.smithy.model.shapes.SetShape;
 import software.amazon.smithy.model.shapes.Shape;
 import software.amazon.smithy.model.shapes.StructureShape;
 import software.amazon.smithy.model.shapes.UnionShape;
@@ -171,9 +173,10 @@ void deserializeNamedMember(
             writer.openBlock("if ($L.$L === \"\") {", "}", inputLocation, locationName, () -> {
                 if (target instanceof MapShape) {
                     writer.write("contents.$L = {};", memberName);
-                }
-                if (target instanceof CollectionShape) {
+                } else if (target instanceof ListShape) {
                     writer.write("contents.$L = [];", memberName);
+                } else if (target instanceof SetShape) {
+                    writer.write("contents.$L = new Set([]);", memberName);
                 }
             });
         }