This is a tracking category for CS1 citations that have empty parameter whose names are not known.
|<param>=|<param1>=, |<param2>=, ...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 Unknown parameter |xxxx= ignored.
Empty positional parameters, which typically look like two adjacent pipes in a template, | |, or a pipe and then the end of the template, |}}, are identified as numbered parameters: |1=. Similarly, a pipe followed by an HTML comment that encloses everything before the next pipe or closing brace, | <!--<param name/value pair>--> | 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: |= or | = → |(empty string)=. Various templates that wrap CS1|2 templates may cause this error when they use constructs like this: |{{#if:{{{2|}}}|title}}={{{2|}}}. When {{{2|}}} does not have a value, the template creates |=.
To resolve this error:
Pages with this error are automatically placed in Category:CS1 errors: empty unknown parameters.