magento#14510: Creating custom customer attribute with default value 0 will cause not saving value for customer entity.

- fix default value check in case of type conversion;
- add boolean attribute default value assignment;

Author: al.kravchuk

app/code/Magento/Catalog/Model/Product/Attribute/Backend/Boolean.php

@@ -25,7 +25,9 @@ public function beforeSave($object)
         $attributeCode = $this->getAttribute()->getName();
         if ($object->getData('use_config_' . $attributeCode)) {
             $object->setData($attributeCode, BooleanSource::VALUE_USE_CONFIG);
+            return $this;
         }
-        return $this;
+
+        return parent::beforeSave($object);
     }
 }

app/code/Magento/Eav/Model/Entity/Attribute/AbstractAttribute.php

@@ -383,7 +383,7 @@ public function getIsVisibleOnFront()
     }
 
     /**
-     * @return string|int|bool|float
+     * @return string|null
      * @codeCoverageIgnore
      */
     public function getDefaultValue()

app/code/Magento/Eav/Model/Entity/Attribute/Backend/AbstractBackend.php

@@ -203,12 +203,12 @@ public function getEntityValueId($entity)
     /**
      * Retrieve default value
      *
-     * @return mixed
+     * @return string
      */
     public function getDefaultValue()
     {
         if ($this->_defaultValue === null) {
-            if ($this->getAttribute()->getDefaultValue()) {
+            if ($this->getAttribute()->getDefaultValue() !== null) {
                 $this->_defaultValue = $this->getAttribute()->getDefaultValue();
             } else {
                 $this->_defaultValue = "";
@@ -280,7 +280,7 @@ public function afterLoad($object)
     public function beforeSave($object)
     {
         $attrCode = $this->getAttribute()->getAttributeCode();
-        if (!$object->hasData($attrCode) && $this->getDefaultValue()) {
+        if (!$object->hasData($attrCode) && $this->getDefaultValue() !== '') {
             $object->setData($attrCode, $this->getDefaultValue());
         }