Checking if Parameter is Empty/Null

Belch · April 13th, 2016, 09:27 AM

Hi,

I have an XSLT parameter which is defined but not given an initial value (the parameter is populated by a webapp we don't have control over and which doesn't always send a value).

When it does have a value, it is an XML document which we can then run Xpath queries against.

What is the best way to check if this parameter is empty/null?
I'm initially doing a string-length command to check if it is > 0, but I'm also not sure that when the parameter is populated with an XML document it returns a string length of over zero.

Thanks,
Neil

Martin Honnen · April 13th, 2016, 09:37 AM

Is that XSLT 1.0 or 2.0? Can you change the XSLT to have

Code:

<xsl:param name="param-name" select="/.."/>

as the default value? That would be an empty node set so you could check

Code:

<xsl:if test="not($param-name)">...</xsl:if>

to check for that empty node set as a default.

In case of XSLT 1.0, check whether the processor supports http://exslt.org/exsl/functions/object-type/index.html, if so you can check

Code:

<xsl:param name="param-name"/>...
<xsl:if test="exsl:object-type($param-name) = 'string' and $param-name = ''">...</xsl:if>

, with XSLT 2.0 you can use

Code:

<xsl:param name="param-name"/>...
<xsl:if test="$param-name instance of xs:string and $param-name = ''">...</xsl:if>

Belch · April 13th, 2016, 10:46 AM

Hi Martin, thanks for your reply.

I see what you mean, however the parameter is actually pre-populated outside of the transform stylesheet so I can't set a default value (as this would override that preset value).
The problem is that the parameter is not always pre-populated, and I need to test for those instances.

Martin Honnen · April 13th, 2016, 10:55 AM

If a parameter is not set, it has an empty string as its value, see the two checks I suggested.