Apply suggestions from code review

Co-authored-by: Micah Parks <66095735+MicahParks@users.noreply.github.com>

parser.go

@@ -89,7 +89,7 @@ func (p *Parser) ParseWithClaims(tokenString string, claims Claims, keyFunc Keyf
 	if !p.SkipClaimsValidation {
 		// Make sure we have at least a default validator
 		if p.validator == nil {
-			p.validator = DefaultValidator
+			p.validator = NewValidator()
 		}
 
 		if err := p.validator.Validate(claims); err != nil {

parser_option.go

@@ -28,6 +28,7 @@ func WithoutClaimsValidation() ParserOption {
 	}
 }
 
+// WithValidator is an option to include a claims validator.
 func WithValidator(v *Validator) ParserOption {
 	return func(p *Parser) {
 		p.validator = v

validator.go

@@ -42,6 +42,7 @@ func NewValidator(opts ...ValidatorOption) *Validator {
 	return v
 }
 
+// Validate validates the given claims. It will also perform any custom validation if claims implements the CustomValidator interface.
 func (v *Validator) Validate(claims Claims) error {
 	var now time.Time
 	vErr := new(ValidationError)
@@ -156,7 +157,7 @@ func verifyAud(aud []string, cmp string, required bool) bool {
 	}
 
 	// case where "" is sent in one or many aud claims
-	if len(stringClaims) == 0 {
+	if stringClaims == "" {
 		return !required
 	}