Issues with Pivot Cache
`CT_pCDSDTCEntries` Elements are choice, so should `allow_none`
`CT_Tuple` only `item` is required, rest should allow none.
Spec:
```
<complexType name="CT_PCDSDTCEntries">
<choice maxOccurs="unbounded">
<element name="m" type="CT_Missing"/>
<element name="n" type="CT_Number"/>
<element name="e" type="CT_Error"/>
<element name="s" type="CT_String"/>
</choice>
<attribute name="count" type="xsd:unsignedInt"/>
</complexType>
```
```
<complexType name="CT_Tuple">
<attribute name="fld" type="xsd:unsignedInt"/>
<attribute name="hier" type="xsd:unsignedInt"/>
<attribute name="item" type="xsd:unsignedInt" use="required"/>
</complexType>
```
Sample file:[sample5.xlsx](/uploads/406f96401e8974ba8a18f5e7a6744679/sample5.xlsx)
Tracking here so I don't lose it. I'll submit the merge on 3.1?
issue