The incoming SOAP message:
<env:Envelope xmlns:env='http://schemas.xmlsoap.org/soap/envelope/'>
<env:Header/>
<env:Body>
<ns1:getPortletProperties xmlns:ns1='urn:oasis:names:tc:wsrp:v1:types' xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'><ns1:registrationContext xsi:nil='1'/><ns1:portletContext><ns1:portletHandle xmlns:ns1='urn:oasis:names:tc:wsrp:v1:types'>/test-basic-portlet.Simple Test Portlet</ns1:portletHandle></ns1:portletContext><ns1:userContext xsi:nil='1'/><ns1:names xsi:nil='1'/></ns1:getPortletProperties>
</env:Body></env:Envelope>

results in a GetPortletProperties object containing a names value being a String[] of size 1 with null elements.

Here's the type definition for the getPortletProperties element:
<element name="getPortletProperties">
<complexType>
<sequence>
<element name="registrationContext" type="types:RegistrationContext" nillable="true"/>
<element name="portletContext" type="types:PortletContext"/>
<element name="userContext" type="types:UserContext" nillable="true"/>
<element name="names" type="xsd:string" nillable="true" maxOccurs="unbounded"/>
</sequence>
</complexType>
</element>

I expect names to be null, not of size 1 with null elements.