🐛 fix: Add nil check for xaiResponse.Usage before calculating CompletionTokens

relay/channel/xai/text.go

@@ -90,8 +90,10 @@ func xAIHandler(c *gin.Context, info *relaycommon.RelayInfo, resp *http.Response
 	if err != nil {
 		return nil, types.NewError(err, types.ErrorCodeBadResponseBody)
 	}
-	xaiResponse.Usage.CompletionTokens = xaiResponse.Usage.TotalTokens - xaiResponse.Usage.PromptTokens
-	xaiResponse.Usage.CompletionTokenDetails.TextTokens = xaiResponse.Usage.CompletionTokens - xaiResponse.Usage.CompletionTokenDetails.ReasoningTokens
+	if xaiResponse.Usage != nil {
+		xaiResponse.Usage.CompletionTokens = xaiResponse.Usage.TotalTokens - xaiResponse.Usage.PromptTokens
+		xaiResponse.Usage.CompletionTokenDetails.TextTokens = xaiResponse.Usage.CompletionTokens - xaiResponse.Usage.CompletionTokenDetails.ReasoningTokens
+	}
 
 	// new body
 	encodeJson, err := common.Marshal(xaiResponse)