Help: CS1 errors

==<span id="param_unknown_empty">Cite has empty unknown parameter: &lt;param></span>==
<section begin="param_unknown_empty_help_text" />{{help desk}}{{plainlist|
*{{#invoke:Cs1 documentation support|help_text_error_messages|err_param_unknown_empty|$1=_|$2=<code class="cs1-code">{{pipe}}&lt;param>=</code>}}
*{{#invoke:Cs1 documentation support|help_text_error_messages|err_param_unknown_empty|$1=s|$2=<code class="cs1-code">{{pipe}}&lt;param1>=</code>, <code class="cs1-code">{{pipe}}&lt;param2>=</code>, ...}}}}

This error message highlights CS1|2 templates that hold empty parameters with names that are not known to a given CS1|2 template.  This error message is a companion to [[Help:CS1 errors#parameter_ignored|Unknown parameter {{pipe}}xxxx= ignored]].

Empty positional parameters, which typically look like two adjacent pipes in a template, <code><nowiki>| |</nowiki></code>, or a pipe and then the end of the template, <code><nowiki>|}}</nowiki></code>, are identified as numbered parameters: {{error-small|{{para|1|plain=yes}}}}.  Similarly, a pipe followed by an HTML comment that encloses everything before the next pipe or closing brace, <code>| &lt;!--&lt;{{var|param name/value pair}}>--> |</code> will be identified as an empty numbered parameter. Parameters that have both a pipe and an equal sign but do not have a name are identified as empty-string parameters: <code>|=</code> or <code>| =</code> → {{error-small|{{para|(empty string)|plain=yes}}}}.  Various templates that wrap CS1|2 templates may cause this error when they use constructs like this: <code><nowiki>|{{#if:{{{2|}}}|title}}={{{2|}}}</nowiki></code>.  When <code><nowiki>{{{2|}}}</nowiki></code> does not have a value, the template creates <code>|=</code>.

To resolve this error: 
* remove the extra pipe, 
* correct the parameter name, 
* remove the parameter from the CS1|2 template, or
* change the citation to use a more appropriate template (e.g. change {{tl|Cite document}} to {{tl|Cite web}})

Pages with this error are automatically placed in {{#invoke:cs1 documentation support|help_text_cats|err_param_unknown_empty|pages=yes}}.<ref group="lower-alpha" name="categories" /><section end="param_unknown_empty_help_text" />