Your environment

• Version of jquery-validate: v1.19.3
• Browser name and version: firefox 109.0.1

Current behavior

When using rule lessThan comparing to an empty field, error is triggered.

Expected behavior

Error should only be triggered if both fields are populated; user could/should add required to the other field if necessary.

Live demo

QUnit.test( "form(): with lessThan", function( assert ) {
	assert.expect( 2 );
	var form = $( "#testForm5" )[ 0 ],
		v = $( form ).validate();

	$( "#x1, #x2" ).val( "hi" );
	assert.ok( v.form(), "Valid form" );
	$( "#y2" ).val( "" );
	assert.ok( v.form(), "Valid form" );
} );