Fix UninitializedProperty 2x

modules/core/lib/Auth/Process/AttributeValueMap.php

@@ -20,13 +20,13 @@ class AttributeValueMap extends \SimpleSAML\Auth\ProcessingFilter
      * The name of the attribute we should assign values to (ie: the target attribute).
      * @var string
      */
-    private $targetattribute;
+    private $targetattribute = '';
 
     /**
      * The name of the attribute we should create values from.
      * @var string
      */
-    private $sourceattribute;
+    private $sourceattribute = '';
 
     /**
      * The required $sourceattribute values and target affiliations.
@@ -92,10 +92,10 @@ class AttributeValueMap extends \SimpleSAML\Auth\ProcessingFilter
         }
 
         // now validate it
-        if (!is_string($this->sourceattribute)) {
+        if (!empty($this->sourceattribute)) {
             throw new Error\Exception("AttributeValueMap: 'sourceattribute' configuration option not set.");
         }
-        if (!is_string($this->targetattribute)) {
+        if (!empty($this->targetattribute)) {
             throw new Error\Exception("AttributeValueMap: 'targetattribute' configuration option not set.");
         }
         if (!is_array($this->values)) {