diff --git a/composer.json b/composer.json
index 273cbc8..a36b88a 100644
--- a/composer.json
+++ b/composer.json
@@ -12,6 +12,9 @@
     "minimum-stability": "dev",
     "prefer-stable": true,
     "config": {
+        "platform": {
+            "php": "7.4.0"
+        },
         "optimize-autoloader": true,
         "sort-packages": true
     },
diff --git a/src/Option.php b/src/Option.php
index 0c347d2..f65895f 100644
--- a/src/Option.php
+++ b/src/Option.php
@@ -244,7 +244,8 @@ public function isType($type)
 
     public function getTypeClass()
     {
-        $class = 'GetOptionKit\\ValueType\\'.ucfirst($this->isa).'Type';
+        $isa = (string) $this->isa;
+        $class = 'GetOptionKit\\ValueType\\'.ucfirst($isa).'Type';
         if (class_exists($class, true)) {
             return new $class($this->isaOption);
         }
@@ -261,7 +262,9 @@ protected function _preprocessValue($value)
     {
         $val = $value;
 
-        if ($isa = ucfirst((string) $this->isa)) {
+        $isa = (string) $this->isa;
+        if ($isa !== '') {
+            $isa = ucfirst($isa);
             $type = $this->getTypeClass();
             if ($type->test($value)) {
                 $val = $type->parse($value);