Spark UDF找不到参数num的隐含值：Numeric [Nothing]

我正在尝试编写泛型add方法，可以采用任何参数类型并返回该类型的结果

def addExactUDFT(implicit num: Numeric[T]): T = {

import num._
x + y

}

def addExact(value1: Column, value2: Column, dataType: String): Column =

dataType match {
  case "Int" => expr(s"addExactUDF(cast($value1 AS INT), cast($value2 AS INT))")
  case "Double" => expr(s"addExactUDF(cast($value1 AS DOUBLE), cast($value2 AS DOUBLE))")
}

现在，当我尝试注册UDF时

object FilterFunctionsUtil extends MathFunctionsNameSpace with StringFunctionsNameSpace {
lazy val registerAsSparkUdf: UserDefinedFunction = {

val sqlContext = SparkSessionFactory.getSparkSession(Map(), Nil).sqlContext

sqlContext.udf.register("addExactUDF", addExactUDF _)
sqlContext.udf.register("subtractExactUDF", subtractExactUDF _)

}
}
它给我带来了错误

Error:(36, 44) could not find implicit value for parameter num: Numeric[Nothing]

    sqlContext.udf.register("addExactUDF", addExactUDF _)

Error:(36, 44) not enough arguments for method addExactUDF: (implicit num: Numeric[Nothing])Nothing.
Unspecified value parameter num.

sqlContext.udf.register("addExactUDF", addExactUDF _)

如何添加隐式以使其工作