According to the HTML5 standard, the value of the id attribute of an element must contain at least one character, and must not contain any space characters. ID attributes that do not conform to this restriction may be interpreted differently by different browsers, and may indicate a misunderstanding on the part of the developer.

Inspect the ID attribute in question. If its value is empty, the attribute is most likely useless and can be removed. If it contains a space, perhaps the attribute was meant to be a class attribute.

The following HTML element has an ID attribute with a space in it:

Most likely this was meant to be a class attribute, like this:

HTML5 Standard: 3.2.5.1 The id attribute.