Fix instances.create to send empty arrays instead of null for volume params (#68)

* Fix instances.create to send empty arrays instead of null for volumes parameters

When volumes or existing_volumes parameters are None, send empty arrays []
to the REST API instead of null values. This ensures API compatibility and
proper validation.

Fixes #56

* Update verda/instances/_instances.py

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Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Alexey Shamrin <shamrin@gmail.com>

Author: 3 people

verda/instances/_instances.py

@@ -171,8 +171,8 @@ def create(
             'description': description,
             'location_code': location,
             'os_volume': os_volume,
-            'volumes': volumes,
-            'existing_volumes': existing_volumes,
+            'volumes': volumes or [],
+            'existing_volumes': existing_volumes or [],
             'is_spot': is_spot,
             'coupon': coupon,
         }