Fixes sending pubsub events for empty item.

[damencho]

XEP-0060 allows no elements on second level of nodes.

[Flowdalic]

Could you provide a pointer to the related section of xep60? I assume it's not an issue that we skip the getElementName().equals(secondElement) check if secondLevelList.isEmpty()? (BTW, why use size() == 0 and not isEmpty()?)

[damencho]

No reason for the size(), you are right.
This is for example in case of: new EventContentFilter(EventElementType.items.toString(), "item")
Where items can have no item children, as said in XEP-0060:

<xs:element name='items'>
    <xs:complexType>
      <xs:choice>
        <xs:element ref='item' minOccurs='0' maxOccurs='unbounded'/>
        <xs:element ref='retract' minOccurs='0' maxOccurs='unbounded'/>
      </xs:choice>
      <xs:attribute name='node' type='xs:string' use='required'/>
    </xs:complexType>
  </xs:element>

[Flowdalic]

Cherry picked, added more strictness and committed as 46f0110