[jboss-user] [JBoss Tools Users] - birt : isnull attribute utility in p:param tag

[gonzalad]

Hello,

I don't understand very well the utility of isnull attribute in the JSF BIRT p:param tag.

For instance, I have the following code :

  | <b:birt designType="embed" designName="test.rptdesign" embeddable="true" masterpage="false">
  | 	<b:param name="clientId" value="#{client.id}" isnull="#{client.id == null}"/>
  | </b:birt>
  | 

Why use a isnull attribute ? If client.id is null, I should theorically use :
<b:birt designType="embed" designName="test.rptdesign" embeddable="true" masterpage="false">
  | 	<b:param name="clientId" value="#{client.id}"/>
  | </b:birt>

>From BIRT documentation http://www.eclipse.org/birt/phoenix/deploy/viewerUsage.php#command_options, I see :
anonymous wrote : 
  | The __isnull Option Report parameters can take a value, or can be null. (Here "null" means the database definition: the value is unknown.) By definition, date and numeric report parameters have a null value if the report parameter is provided in the URL, and the value is blank. However, string report parameters have an ambiguity: is an empty value to be considered blank (a string whose value is ""), or null? Since blank is used more often, BIRT interprets an empty report parameter value as blank. To say a string parameter is is null, just write:
  | 
  |     __isnull=yourParam 
  | 
  | While this option is primarily for string report parameters, it works just as well for other report parameter types as well. See the Report Parameters section below for additional details. 
  | 

But I doesn't help me to really understand why we have isnull attribute in the JSF tag.

If anyone has some insights about it, thanks !

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