title: SSRS 2017: Want to set a parameter to a default of NULL in a shared dateaset
body: <h2>the problem</h2>
  <p>I have a problem with a SSRS 2017 shared dataset.</p>
  <p>This dataset is calling a stored procedure. One of the SP's parameters is of type <code>DateTime</code>. Within the dataset's parameters dialog I've set the default to <code>(Null)</code>. But this seems to be ignored...</p>
  <p>With paginated reports everything works fine. The defined report parameters (or <em>built-in</em> parameters) can be used to pass valid values.</p>
  <p>But when I try to use this dataset within a mobile report I get an error. I cannot even add the dataset! After quite some search I found, that the SP was called with a blank instead of <code>NULL</code> (<em>Pofiler tells me</em>: <code>,@ClientTime=N''</code>), hence the type conversion to <code>DateTime</code> failed.</p>
  <p>I do not want to change this parameter to a string type, because this report will run in various environments. The correct date getting into the stored proc if taken as string is really awful: <code>Nov 14 2017  3:35PM</code> (culture and language dependant!) I do not want to rely on any conversion from string!</p>
  <h2>the question</h2>
  <p>How can I force a SSRS shared dataset to use a real <code>NULL</code> for a parameter?</p>