How to null out a value using xml integration

Hi,

Can anyone tell me what I am doing wrong? I am trying to null out the Release's headers flexFields (all of them). It work for the <FlexFieldStrings> and <FlexFieldDates> but not the <FlexFieldNumbers>. Any suggestions? I am using OTM 6.3.3

Sample XML:
<Release>
<ReleaseGid>
<Gid>
<DomainName>companyName</DomainName>
<Xid>2234567890</Xid>
</Gid>
</ReleaseGid>
<TransactionCode>UI</TransactionCode>
<ReleaseHeader>
<FlexFieldStrings>
<Attribute2>~</Attribute2>
<Attribute3>~</Attribute3>
<Attribute4>~</Attribute4>
<Attribute5>~</Attribute5>
<Attribute6>~</Attribute6>
</FlexFieldStrings>
<FlexFieldNumbers>
<AttributeNumber7>~</AttributeNumber7>
<AttributeNumber8>~</AttributeNumber8>
<AttributeNumber9>~</AttributeNumber9>
</FlexFieldNumbers>
<FlexFieldDates>
<AttributeDate2>
<GLogDate>~</GLogDate>
</AttributeDate2>
<AttributeDate3>
<GLogDate>~</GLogDate>
</AttributeDate3>
<AttributeDate4>
<GLogDate>~</GLogDate>
</AttributeDate4>
<AttributeDate5>
<GLogDate>~</GLogDate>
</AttributeDate5>
<AttributeDate6>
<GLogDate>~</GLogDate>
</AttributeDate6>
</FlexFieldDates>
</ReleaseHeader>
</Release>