code: def fill_median(df, columns):
      return callZooFunc("float", "fillMedian", df, columns)
  
imports: from zoo.common.utils import callZooFunc
  from pyspark.sql.types import IntegerType, ShortType, LongType, FloatType, DecimalType, DoubleType
label_desc: Use image node_id 7 for calling a global function with example usage: fill_median(df, columns) and returns: callZooFunc