EC2::DescribeVpcs uses incorrect MaxResults value by default

[ianbotsf]

Describe the bug

Calling EC2's DescribeVpcs API without providing an explicit MaxResults causes an error about the parameter being invalid.

Expected behavior

The operation should succeed even when no parameters (including MaxResults) are passed.

Current behavior

The operation fails:

Exception in thread "main" aws.sdk.kotlin.services.ec2.model.Ec2Exception: Value ( 0 ) for parameter MaxResults is invalid. Expecting a value greater than or equal to 5.
	at aws.sdk.kotlin.services.ec2.transform.DescribeVpcsOperationDeserializerKt.throwDescribeVpcsError(DescribeVpcsOperationDeserializer.kt:64)
	at aws.sdk.kotlin.services.ec2.transform.DescribeVpcsOperationDeserializerKt.access$throwDescribeVpcsError(DescribeVpcsOperationDeserializer.kt:1)
	at aws.sdk.kotlin.services.ec2.transform.DescribeVpcsOperationDeserializerKt$throwDescribeVpcsError$1.invokeSuspend(DescribeVpcsOperationDeserializer.kt)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
	at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:284)
	at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:85)
	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:59)
	at kotlinx.coroutines.BuildersKt.runBlocking(Unknown Source)
	at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt:38)
	at kotlinx.coroutines.BuildersKt.runBlocking$default(Unknown Source)
	at foo.ScratchKt.main(Scratch.kt:8)
	at foo.ScratchKt.main(Scratch.kt)

Steps to Reproduce

Execute this code:

fun main(): Unit = runBlocking {
    Ec2Client.fromEnvironment().use { ec2 ->
        ec2.describeVpcs().vpcs?.forEach { println(it) }
    }
}

Possible Solution

No response

Context

This same code runs successfully in 0.21.0-beta. Note that in that version, the body of the POST request is:

Action=DescribeVpcs&Version=2016-11-15

Note that no explicit MaxResults is specified in the body, which is correct.

In 0.29.1-beta, the body of the POST request is:

Action=DescribeVpcs&Version=2016-11-15&DryRun=false&MaxResults=0

Note that MaxResults=0 is included and is clearly erroneous.

AWS Kotlin SDK version used

0.29.1-beta

Platform (JVM/JS/Native)

OpenJDK Runtime Environment Corretto-17.0.8.7.1 (build 17.0.8+7-LTS)

Operating System and version

Amazon Linux 2

[ianbotsf]

The MaxResults field in the Smithy model:

"MaxResults": {
    "target": "com.amazonaws.ec2#DescribeVpcsMaxResults",
    "traits": {
        "smithy.api#clientOptional": {},
        "smithy.api#default": 0,
        "smithy.api#documentation": "(omitted)"
    }
}

The clientOptional annotation should supercede the default trait but currently the SDK is incorrectly serializing MaxResults=0 in the request.

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