[SPARK-28702][SQL] Display useful error message (instead of NPE) for …

…invalid Dataset operations

### What changes were proposed in this pull request?
Added proper message instead of NPE for invalid Dataset operations (e.g. calling actions inside of transformations) similar to SPARK-5063 for RDD

### Why are the changes needed?
To report the user about the exact issue instead of NPE

### Does this PR introduce any user-facing change?
No

### How was this patch tested?

Manually tested

```scala
test code snap
"import spark.implicits._
    val ds1 = spark.sparkContext.parallelize(1 to 100, 100).toDS()
    val ds2 = spark.sparkContext.parallelize(1 to 100, 100).toDS()
    ds1.map(x => {
      // scalastyle:off
      println(ds2.count + x)
      x
    }).collect()"
```

Closes apache#25503 from shivusondur/jira28702.

Authored-by: shivusondur <[email protected]>
Signed-off-by: Josh Rosen <[email protected]>

sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala

@@ -26,7 +26,7 @@ import scala.util.control.NonFatal
 
 import org.apache.commons.lang3.StringUtils
 
-import org.apache.spark.TaskContext
+import org.apache.spark.{SparkException, TaskContext}
 import org.apache.spark.annotation.{DeveloperApi, Evolving, Experimental, Stable, Unstable}
 import org.apache.spark.api.java.JavaRDD
 import org.apache.spark.api.java.function._
@@ -184,11 +184,23 @@ private[sql] object Dataset {
  */
 @Stable
 class Dataset[T] private[sql](
-    @transient val sparkSession: SparkSession,
+    @transient private val _sparkSession: SparkSession,
     @DeveloperApi @Unstable @transient val queryExecution: QueryExecution,
     @DeveloperApi @Unstable @transient val encoder: Encoder[T])
   extends Serializable {
 
+  @transient lazy val sparkSession: SparkSession = {
+    if (_sparkSession == null) {
+      throw new SparkException(
+      "Dataset transformations and actions can only be invoked by the driver, not inside of" +
+        " other Dataset transformations; for example, dataset1.map(x => dataset2.values.count()" +
+        " * x) is invalid because the values transformation and count action cannot be " +
+        "performed inside of the dataset1.map transformation. For more information," +
+        " see SPARK-28702.")
+    }
+    _sparkSession
+  }
+
   // A globally unique id of this Dataset.
   private val id = Dataset.curId.getAndIncrement()