getPersistentRDDs returns Map of cached RDDs and DataFrames in Spark 2.2.0, but in Spark 2.4.7 - it returns Map of cached RDDs only

Question

If cache RDD and DataFrame in Spark version 2.2.0 getPersistentRDDs returns Map size 2:

scala> val rdd = sc.parallelize(Seq(1))
rdd: org.apache.spark.rdd.R