ValueValidator.php

<?php

class ValueValidator {
    public static function checkEmpty($value) {
        return (empty($value)) ? true : false;
    }

    public static function checkIsset($value) {
        return (isset($value)) ? true : false;
    }

    public static function checkIsNull($value) {
        return (is_null($value)) ? true : false;
    }

    public static function equalsStrictEmpty($value) {
        return ($value === '') ? true : false;
    }

    public static function equalsStrictNull($value) {
        return ($value === null) ? true : false;
    }

    public static function equalsLooseEmpty($value) {
        return ($value == '') ? true : false;
    }

    public static function equalsLooseNull($value) {
        return ($value == null) ? true : false;
    }

    public static function validateValue($value) {
        if (is_string($value) || $value === null || $value === false || $value === true) {
            switch ($value) {
                case $value === null:
                    $printedValue = 'null';
                    break;
                case $value === false:
                    $printedValue = 'false';
                    break;
                case $value === true;
                    $printedValue = 'true';
                    break;
                default:
                    $printedValue = $value;
            }

            echo (ValueValidator::checkEmpty($value)) ? "empty($printedValue) = TRUE\n" : "empty($printedValue) = FALSE\n";
            echo (ValueValidator::equalsStrictEmpty($value)) ? "$printedValue === '' =  TRUE\n" : "$printedValue === '' = FALSE\n";
            echo (ValueValidator::equalsLooseEmpty($value)) ? "$printedValue == '' =  TRUE\n" : "$printedValue == '' = FALSE\n";
            echo (ValueValidator::checkIsNull($value)) ? "is_null($printedValue) = TRUE\n" : "is_null($printedValue) = FALSE\n";
            echo (ValueValidator::equalsStrictNull($value)) ? "$printedValue === null = TRUE\n" : "$printedValue === null = FALSE\n";
            echo (ValueValidator::equalsLooseNull($value)) ? "$printedValue == null = TRUE\n" : "$printedValue == null = FALSE\n";
            echo (ValueValidator::checkIsset($value)) ? "isset($printedValue) = TRUE\n" : "isset($printedValue) = FALSE\n";

        } else {
            echo "Check PHP error log for results\n";
            error_log('$value provided is ' . print_r($value, true));
            (ValueValidator::checkEmpty($value)) ? error_log('empty($value) = TRUE') : error_log('empty($value) = FALSE');
            (ValueValidator::equalsStrictEmpty($value)) ? error_log('$value === "" =  TRUE') : error_log('$value === "" = FALSE');
            (ValueValidator::equalsLooseEmpty($value)) ? error_log('$value == "" =  TRUE') : error_log('$value == "" = FALSE');
            (ValueValidator::checkIsNull($value)) ? error_log('is_null($value) = TRUE') : error_log('is_null($value) = FALSE');
            (ValueValidator::equalsStrictNull($value)) ? error_log('$value === null = TRUE') : error_log('$value === null = FALSE');
            (ValueValidator::equalsLooseNull($value)) ? error_log('$value == null = TRUE') : error_log('$value == null = FALSE');
            (ValueValidator::checkIsset($value)) ? error_log('isset($value) = TRUE') : error_log('isset($value) = FALSE');
        }
    }
}

// Examples
$values = ['', null, false, true, [], ['123']];

foreach ($values as $value) {
    ValueValidator::validateValue($value);
}