If environment variable does not exist, the value of property using this environment should not be NULL.

Extension might uses the environment variable as the value of property, ex:

"property": {
      "api_key": "${env:BING_API_KEY}"
 }

If the environment variable does not exist, the ten_value_t bound to this property is TEN_TYPE_NULL.

• Call get_property_string() from Python, PyUnicode_FromString will be crashed if the value is NULL.
• Schema conversion will be failed if the value type is TEN_TYPE_NULL.

It's better to set the default value to an empty string rather than NULL if the environment does not exist.

Start by tracing environment-variable property resolution, then inspect the get_property_string() Python entry point and schema conversion path mentioned in the issue. The change is complete when a missing environment variable resolves to an empty string rather than TEN_TYPE_NULL, without crashing Python conversion or failing schema conversion.