Update serializing empty lists for query protocols

Update serializing empty lists for query protocols (see references)
to pass protocol tests.

Previous Behavior:

`{ "ListArg": [] }` serializes to ``.

Current Behavior:

`{ "ListArg": [] }` serializes to `?ListArg=`.

References:

- smithy-lang/smithy#1444
- [AWS query
  protocol](https://awslabs.github.io/smithy/2.0/aws/protocols/aws-query-protocol.html)
- [AWS EC2 query
  protocol](https://awslabs.github.io/smithy/2.0/aws/protocols/aws-ec2-query-protocol.html)

aws/protocol/query/array.go

@@ -59,3 +59,20 @@ func (a *Array) Value() Value {
 	// Lists can't have flat members
 	return newValue(a.values, fmt.Sprintf("%s.%d", prefix, a.size), false)
 }
+
+// Empty allows empty Query Array URI encoding, e.g.
+//
+//	"ListArg": [] -> ?ListArg=
+//
+// If this method is not called on an empty Query Array, it will
+// not be serialized when encoded.
+//
+// The method should ONLY be used if the Array is known to be empty.
+func (a *Array) Empty() {
+	// If the Array is not empty, return to avoid wrong encoding
+	if a.size != 0 {
+		return
+	}
+	// Set value of prefix to empty string (no text)
+	newValue(a.values, a.prefix, false).String("")
+}

aws/protocol/query/encoder_test.go

@@ -35,6 +35,14 @@ func TestEncode(t *testing.T) {
 			},
 			Expect: []byte(`list.spam.1=spam&list.spam.2=eggs`),
 		},
+		"empty list": {
+			Encode: func(e *Encoder) error {
+				list := e.Object().Key("ListArg").Array("member")
+				list.Empty()
+				return e.Encode()
+			},
+			Expect: []byte(`ListArg=`),
+		},
 		"flat list": {
 			Encode: func(e *Encoder) error {
 				list := e.Object().FlatKey("list").Array("spam")
@@ -44,6 +52,14 @@ func TestEncode(t *testing.T) {
 			},
 			Expect: []byte(`list.1=spam&list.2=eggs`),
 		},
+		"empty flat list": {
+			Encode: func(e *Encoder) error {
+				list := e.Object().FlatKey("ListArg").Array("member")
+				list.Empty()
+				return e.Encode()
+			},
+			Expect: []byte(`ListArg=`),
+		},
 		"map": {
 			Encode: func(e *Encoder) error {
 				mapValue := e.Object().Key("map").Map("key", "value")

codegen/smithy-aws-go-codegen/src/main/java/software/amazon/smithy/aws/go/codegen/QueryShapeSerVisitor.java

@@ -23,6 +23,7 @@
 import software.amazon.smithy.model.shapes.MapShape;
 import software.amazon.smithy.model.shapes.MemberShape;
 import software.amazon.smithy.model.shapes.Shape;
+import software.amazon.smithy.model.shapes.ShapeType;
 import software.amazon.smithy.model.shapes.StructureShape;
 import software.amazon.smithy.model.shapes.UnionShape;
 import software.amazon.smithy.model.traits.EnumTrait;
@@ -75,10 +76,16 @@ protected void serializeCollection(GenerationContext context, CollectionShape sh
         MemberShape member = shape.getMember();
         Shape target = context.getModel().expectShape(member.getTarget());
 
-        // If the list is empty, exit early to avoid extra effort.
-        writer.write("if len(v) == 0 { return nil }");
+        String arrayName = getSerializedLocationName(member, "member");
+
+        // If the list is empty, serialize an empty query value.
+        writer.write("""
+            if len(v) == 0 {
+                value.Array($S).Empty()
+                return nil
+            }""", arrayName);
 
-        writer.write("array := value.Array($S)", getSerializedLocationName(member, "member"));
+        writer.write("array := value.Array($S)", arrayName);
         writer.write("");
 
         writer.openBlock("for i := range v {", "}", () -> {