Returning NULL to C#-client

Hi! I wrote a PEAR:SOAP webservice reading data out of a database and returning it in form of a struct to a C#-client. The problem is, that C# can't read NULL values for datatypes like INT, DOUBLE etc. When I use the attribute "nil=true" on an element of the struct it works fine, but only with strings. In C# the string in the struct is NULL. But INT, DOUBLE etc are initialized with "0" by C#. How can I return NULL values to the client? I thought about using the SqlTypes, because these are able to get the value NULL. But how can I implement these Types in my PEAR:SOAP webservice? Where do I get such a schema? Or is there any other solution for this problem? Thanks!