A regex should never include a repetitive pattern whose body would match the empty string. This is usually a sign that a part of the regex is redundant or does not do what the author intended.

Noncompliant Code Example

/(?:)*/      // same as the empty regex, the '*' accomplishes nothing
/(?:|x)*/    // same as the empty regex, the alternative has no effect
/(?:x|)*/    // same as 'x*', the empty alternative has no effect
/(?:x*|y*)*/ // same as 'x*', the first alternative would always match, y* is never tried
/(?:x?)*/    // same as 'x*'
/(?:x?)+/    // same as 'x*'

Compliant Solution

/x*/