I have a pyspark dataframe

deviceId    timestamp
009eeb      2024-04-22
009eeb      2024-04-24
7c002v      2024-04-20
7c002v      null
4fd556      null
4fd556      null

I need to get the max timestamp in the final dataframe and drop duplicates.
I tried with the below code

w = Window.partitionBy('deviceId')
df_max = df.withColumn('max_col', F.max('timestamp').over(w))
            .where((F.col('timestamp') == F.col('max_col')) | (F.col('timestamp').isNull()))            
            .dropDuplicates()

But from this code, I’m getting what I need to get.

deviceId    timestamp
009eeb      2024-04-24
7c002v      null
4fd556      null
4fd556      null

I need to get the result as below

deviceId    timestamp
009eeb      2024-04-24
7c002v      2024-04-20
4fd556      null

Please suggest any changes to be done