doc/lit (document/literal) style/use "unable to serialize result"

[blantonl]

When specifying document/literal return types an error is generated:

 <SOAP-ENV:Fault>
         <faultcode xsi:type="xsd:string">SOAP-ENV:Server</faultcode>
         <faultstring xsi:type="xsd:string">unable to serialize result</faultstring>
         <faultactor xsi:type="xsd:string"/>
         <detail xsi:type="xsd:string"/>
      </SOAP-ENV:Fault>

Example:

require_once("nusoap-0.9.17/src/nusoap.php");
$server = new nusoap_server(); // Create a instance for nusoap server

$server->configureWSDL("Soap Demo","urn:soapdemo"); // Configure WSDL file
$namespace = "test";
$server->register(
	"get_price", // name of function
	array("name"=>"xsd:string"),  // inputs
	array("return"=>"xsd:integer"),   // outputs
	false,
	false,
	'document',  // <====
	'literal', // <=====
	'Test Docs'
);

$server->service(file_get_contents("php://input"));

function get_price($name)
{
	$products = [
		"book"=>20,
		"pen"=>10,
		"pencil"=>5
	];

	foreach($products as $product=>$price)
	{
		if($product==$name)
		{
			return $price;
			break;
		}
	}
}