do NOT serialize empty lists in ec2query (#2630)

Author: lucix-aws

.changelog/2781886a806d48bda53e5be2992aa455.json

@@ -0,0 +1,8 @@
+{
+    "id": "2781886a-806d-48bd-a53e-5be2992aa455",
+    "type": "bugfix",
+    "description": "Fix serialization behavior of empty lists.",
+    "modules": [
+        "service/ec2"
+    ]
+}

codegen/gradle.properties

@@ -1,2 +1,2 @@
-smithyVersion=1.47.0
+smithyVersion=1.49.0
 smithyGradleVersion=0.7.0

codegen/smithy-aws-go-codegen/src/main/java/software/amazon/smithy/aws/go/codegen/Ec2QueryShapeSerVisitor.java

@@ -3,8 +3,12 @@
 import java.util.Optional;
 import java.util.function.Predicate;
 import software.amazon.smithy.aws.traits.protocols.Ec2QueryNameTrait;
+import software.amazon.smithy.go.codegen.GoWriter;
 import software.amazon.smithy.go.codegen.integration.ProtocolGenerator.GenerationContext;
+import software.amazon.smithy.go.codegen.knowledge.GoPointableIndex;
+import software.amazon.smithy.model.shapes.CollectionShape;
 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.traits.TimestampFormatTrait.Format;
 import software.amazon.smithy.model.traits.XmlNameTrait;
@@ -51,6 +55,14 @@ protected String getSerializedLocationName(MemberShape memberShape, String defau
                 .orElse(defaultValue));
     }
 
+    // EC2Query specifically does not serialize non-nil, empty lists
+    protected void serializeCollection(GenerationContext context, CollectionShape shape) {
+        context.getWriter().get()
+                .write("if len(v) == 0 { return nil }");
+
+        super.serializeCollection(context, shape);
+    }
+
     @Override
     protected boolean isFlattened(GenerationContext context, MemberShape memberShape) {
         // All lists, sets, and maps are flattened in aws.ec2.