Hi everybody!

When I import data from cosmos db into databricks, and create temporary view from this data, filter "someField IS NOT NULL" is not working correctly. The only way to make it work is to add one more condition "LOWER(CAST(someField AS STRING)) <> 'null'", but it's not correct, because for this field there is not data with string value, it contains json object or NULL.

`connectionConfig = {
"spark.cosmos.accountEndpoint" : "endpoint",
"spark.cosmos.accountKey" : "key",
"spark.cosmos.database" : "database",
"spark.cosmos.container" : "containter",
"spark.cosmos.read.inferSchema.enabled" : "true"
}

spark
.read
.format("cosmos.oltp")
.options(**connectionConfig)
.load()
.createOrReplaceTempView("tmp_cosmos_data")`

Apache Spark 3.1.1
Library: com.azure.cosmos.spark:azure-cosmos-spark_3-1_2-12:4.2.0
Operating System: Ubuntu 18.04.5 LTS
Java: Zulu 8.52.0.23-CA-linux64 (build 1.8.0_282-b08)

If you can't reproduce it on your side with simple execution of mentioned actions please let me know. To fill all the requirements mentioned in this bug report and to meet privacy requirements it's needed to create separate instance of Cosmos DB and so on. Please let me know if it's necessary.

Thanks in advance.

Regards,
Daniil.