[SPARK-12028] [SQL] get_json_object returns an incorrect result when the value is null literals

When calling `get_json_object` for the following two cases, both results are `"null"`:

```scala
    val tuple: Seq[(String, String)] = ("5", """{"f1": null}""") :: Nil
    val df: DataFrame = tuple.toDF("key", "jstring")
    val res = df.select(functions.get_json_object($"jstring", "$.f1")).collect()
```
```scala
    val tuple2: Seq[(String, String)] = ("5", """{"f1": "null"}""") :: Nil
    val df2: DataFrame = tuple2.toDF("key", "jstring")
    val res3 = df2.select(functions.get_json_object($"jstring", "$.f1")).collect()
```

Fixed the problem and also added a test case.

Author: gatorsmile <gatorsmile@gmail.com>

Closes #10018 from gatorsmile/get_json_object.

1 files changed, 5 insertions, 2 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala
index 8cd73236a7..4991b9cb54 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/jsonExpressions.scala
@@ -298,8 +298,11 @@ case class GetJsonObject(json: Expression, path: Expression)
 
       case (FIELD_NAME, Named(name) :: xs) if p.getCurrentName == name =>
         // exact field match
-        p.nextToken()
-        evaluatePath(p, g, style, xs)
+        if (p.nextToken() != JsonToken.VALUE_NULL) {
+          evaluatePath(p, g, style, xs)
+        } else {
+          false
+        }
 
       case (FIELD_NAME, Wildcard :: xs) =>
         // wildcard field match