The following code block contains an error. It is intended to create and register a SQL UDF named "ASSESS_PERFORMANCE" using the Scala function assessPerformance() and apply it to the column customerSatisfaction in the table stores. Identify the error.

Code block:

spark.udf.register("ASSESS_PERFORMANCE", assessPerformance)
spark.sql("SELECT customerSatisfaction, ASSESS_PERFORMANCE(customerSatisfaction) AS result FROM stores")