fix: No-ops instead of encoding empty string when encoding an empty body in xml (#481)

* Removes logic for case where the payload member is nil

* Fixes tests after adjusting HttpBodyMiddleware

* Correctly renders empty bodies

Author: Ed Paulosky

smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/integration/middlewares/handlers/HttpBodyMiddleware.kt

@@ -111,17 +111,11 @@ class HttpBodyMiddleware(
                         renderEncodedBodyAddedToRequest(bodyDeclaration, dataDeclaration)
                     }
                     writer.indent()
-                    writer.openBlock("if encoder is JSONEncoder {", "} else if encoder is XMLEncoder {") {
+                    writer.openBlock("if encoder is JSONEncoder {", "}") {
                         writer.write("// Encode an empty body as an empty structure in JSON")
                         writer.write("let \$L = \"{}\".data(using: .utf8)!", dataDeclaration)
                         renderEncodedBodyAddedToRequest(bodyDeclaration, dataDeclaration)
                     }
-                    writer.indent()
-                    writer.write("// Encode an empty body as an empty string in XML")
-                    writer.write("let \$L = \"\".data(using: .utf8)!", dataDeclaration)
-                    renderEncodedBodyAddedToRequest(bodyDeclaration, dataDeclaration)
-                    writer.dedent()
-                    writer.write("}")
                     writer.dedent()
                     writer.write("}")
                 }

smithy-swift-codegen/src/test/kotlin/HttpBodyMiddlewareTests.kt

@@ -160,11 +160,6 @@ class HttpBodyMiddlewareTests {
                                 let payload1data = "{}".data(using: .utf8)!
                                 let payload1body = ClientRuntime.HttpBody.data(payload1data)
                                 input.builder.withBody(payload1body)
-                            } else if encoder is XMLEncoder {
-                                // Encode an empty body as an empty string in XML
-                                let payload1data = "".data(using: .utf8)!
-                                let payload1body = ClientRuntime.HttpBody.data(payload1data)
-                                input.builder.withBody(payload1body)
                             }
                         }
                     } catch let err {