Given:

<c:set var="varName">
</c:set>

Result:

<h3>Validation error messages from tag library c</h3>
<p>null: A body is necessary inside the "c:set" tag, given its attributes.</p>
<p>null: A body is necessary inside the "c:set" tag, given its attributes.</p>
<p>null: A body is necessary inside the "c:set" tag, given its attributes.</p>


According to the public draft: 

2.5 Body Content, paragraph 1:

   "If an action accepts a body content, an empty body is always valid
    unless explicitly stated otherwise.

    If the body content is used to set the value of an attribute, then
    an emtpy body content sets the attribute value to an empty string."

Also, is the duplicate TLV messages intentional?