Apache Spark SQL UDF to get or default value in Struct, with dot notation path

udf_struct_get.scala

import org.apache.spark.sql.functions.udf
import org.apache.spark.sql.catalyst.expressions.GenericRowWithSchema
import org.apache.spark.sql.Row

spark.udf.register("struct_def", (root:GenericRowWithSchema, path: String, defaultValue: String) => {
    
    var fields = path.split("\\.")
    var buffer:Row = root
    val lastItem = fields.last
    
    fields = fields.dropRight(1)
    
    fields.foreach( (field:String) => {
        if (buffer != null) {
            if (buffer.schema.fieldNames.contains(field)) {
                buffer = buffer.getStruct(buffer.fieldIndex(field))
            } else {
                buffer = null
            }
        }
    })
    
    if (buffer == null) {
        defaultValue
    } else {
        buffer.getString(buffer.fieldIndex(lastItem))
    }
})