Which of the following code blocks returns a new DataFrame where column `sqft` from DataFrame `storesDF` has its null values replaced with the value `30000`? A sample of DataFrame `storesDF` is below: ``` storeId sqft 0 43161 51200 1 51200 null 2 null 78367 3 78367 null ``` | Databricks Certified Associate Developer for Apache Spark Quiz - LeetQuiz