[ISSUE] NullPointerException in UserAgent.env() when PATH environment variable is missing #550

Description
When running on a system where the PATH environment variable is not set, the following code in UserAgent.env() causes a NullPointerException:
System.getenv("PATH").split(File.pathSeparator)
System.getenv("PATH").split(File.pathSeparator)

If System.getenv("PATH") returns null, calling .split() throws an exception.

Reproduction
Unset the PATH environment variable.
Run any code that triggers UserAgent.env().

Expected behavior
The code should handle missing PATH gracefully, e.g., by using an empty array.

Is it a regression?
this is introduced in databricks-sdk-java-0.40.0.jar

Debug Logs

Other Information

• OS: [e.g. macOS]
• Version: I am using 0.67.3 version

Additional context
Add any other context about the problem here.