Help:Cite errors/Cite error references no text

Overview
A footnote used multiple times may be defined with a name:
 * content

To invoke a named footnote:
 * 

References may also be defined within the reference list. Here is a correct example:

Issues and resolution
A named reference was invoked but never defined. The reference may be defined inline or in the reference list. You may have misspelled the reference name, or used special characters that look the same but are actually different. For instance, content and content are not the same: one contains a hyphen while the other uses an ndash. To avoid this sort of error, try to stick to the characters available on the standard keyboard.

You may have also invoked a reference but never defined it, for example:  or.

The full reference may have been removed from the article with other content, such as when removing information under BLP concerns. In this case the text of the reference will be available in the page history, and you can convert the single tag into a full reference.

List-defined references may have this error if:
 * The closing tag is missing or malformed. This would normally result in a  message, but the missing tag causes the reference to "eat" the reference following in the list. Since that reference is undefined, the  for both references. This can be very confusing, as the order of references in the list may not match the order used in the content.
 * If reflist is used and the refs parameter is missing or malformed.

Bugs

 * Some MediaWiki Cite error messages do not allow markup

Standard
Here the reference named minim is invoked, but never defined:

{{pre2| Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.

List-defined references
Here, the referenced named excepteur is improperly closed— it causes the reference following in the list named ipsum to not close, thus both references show an error:

{{pre2| Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. Curabitur pretium tincidunt lacus.