System configuration Validation

This field should be save empty, but incorrect validation was applied. Because of that, admin user couldn't save the empty value.

Author: ejaz-alam

app/code/Magento/Integration/etc/adminhtml/system.xml

@@ -16,7 +16,7 @@
                 <field id="customer" translate="label comment" type="text" sortOrder="30" showInDefault="1" canRestore="1">
                     <label>Customer Token Lifetime (hours)</label>
                     <comment>We will disable this feature if the value is empty.</comment>
-                    <validate>required-entry validate-zero-or-greater validate-number</validate>
+                    <validate>validate-zero-or-greater validate-number</validate>
                 </field>
                 <field id="admin" translate="label comment" type="text" sortOrder="60" showInDefault="1" canRestore="1">
                     <label>Admin Token Lifetime (hours)</label>