Unexpected HTTP response: 500

Request
{
    "operation" => "composite",
    "address" => [],
    "steps" => [
        {
            "address" => [
                ("subsystem" => "datasources"),
                ("data-source" => "ExampleDS")
            ],
            "operation" => "write-attribute",
            "name" => "min-pool-size",
            "value" => undefined
        },
        {
            "address" => [
                ("subsystem" => "datasources"),
                ("data-source" => "ExampleDS")
            ],
            "operation" => "write-attribute",
            "name" => "initial-pool-size",
            "value" => undefined
        },
        {
            "address" => [
                ("subsystem" => "datasources"),
                ("data-source" => "ExampleDS")
            ],
            "operation" => "write-attribute",
            "name" => "max-pool-size",
            "value" => undefined
        },
        {
            "address" => [
                ("subsystem" => "datasources"),
                ("data-source" => "ExampleDS")
            ],
            "operation" => "write-attribute",
            "name" => "capacity-decrementer-properties",
            "value" => {"foo" => "bar"}
        }
    ]
}

Response

Internal Server Error
{
    "outcome" => "failed",
    "result" => {
        "step-1" => {
            "outcome" => "failed",
            "rolled-back" => true
        },
        "step-2" => {
            "outcome" => "failed",
            "failure-description" => "WFLYJCA0045: failed to set attribute: null",
            "rolled-back" => true
        },
        "step-3" => {
            "outcome" => "failed",
            "rolled-back" => true
        },
        "step-4" => {
            "outcome" => "failed",
            "rolled-back" => true
        }
    },
    "failure-description" => {"WFLYCTL0062: Composite operation failed and was rolled back. Steps that failed:" => {"Operation step-2" => "WFLYJCA0045: failed to set attribute: null"}},
    "rolled-back" => true
}