如果列有NULL，如何在Spark中设置默认值？

from pyspark.sql import SparkSession

# 创建SparkSession
spark = SparkSession.builder.getOrCreate()

# 创建示例数据集
data = [("Alice", 25, None),
        ("Bob", 30, None),
        ("Charlie", None, None)]

# 创建DataFrame
df = spark.createDataFrame(data, ["name", "age", "gender"])

# 设置默认值
default_values = {"age": 0, "gender": "Unknown"}
df_filled = df.na.fill(default_values)

# 显示填充后的结果
df_filled.show()

+-------+---+-------+
|   name|age| gender|
+-------+---+-------+
|  Alice| 25|Unknown|
|    Bob| 30|Unknown|
|Charlie|  0|Unknown|
+-------+---+-------+