[ISSUE] SDK throws null pointer exception when attempting to refresh tokens

[satviksr-db]

Description
Dear team,
Sometimes the SDK throws null pointer exception when attempting to refresh tokens, I am not entirely sure if there is an issue with the SDK or the API is behaving incorrectly

Caused by: java.lang.NullPointerException: accessToken must be defined
	at java.base/java.util.Objects.requireNonNull(Objects.java:246)
	at com.databricks.sdk.core.oauth.Token.<init>(Token.java:51)
	at com.databricks.sdk.core.oauth.Token.<init>(Token.java:41)
	at com.databricks.sdk.core.oauth.RefreshableTokenSource.retrieveToken(RefreshableTokenSource.java:74)
	at com.databricks.sdk.core.oauth.ClientCredentials.refresh(ClientCredentials.java:104)
	at com.databricks.sdk.core.oauth.RefreshableTokenSource.getToken(RefreshableTokenSource.java:84)
	at com.databricks.sdk.core.oauth.OAuthM2MServicePrincipalCredentialsProvider.lambda$configure$0(OAuthM2MServicePrincipalCredentialsProvider.java:45)
	at com.databricks.sdk.core.DatabricksConfig.authenticate(DatabricksConfig.java:189)

Reproduction
A minimal code sample demonstrating the bug.

Expected behavior
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Is it a regression?
Did this work in a previous version of the SDK? If so, which versions did you try?

Debug Logs
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Other Information

• OS: [e.g. macOS]
• Version: [e.g. 0.1.0]

Additional context
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