SNOW-1320314: fix Null handling in Variants (#109)

.pre-commit-config.yaml

@@ -1,5 +1,5 @@
 repos:
 - repo: [email protected]:snowflakedb/casec_precommit.git
-  rev: HEAD
+  rev: v1.35.4
   hooks:
   - id: secret-scanner

src/main/scala/com/snowflake/snowpark/types/Variant.scala

@@ -164,7 +164,15 @@ class Variant private[snowpark] (
   def this(str: String) =
     this({
       try {
-        MAPPER.readTree(str)
+        // `ObjectMapper` only reads the first token from
+        // the input string but not the whole string.
+        // For example, It can successfully
+        // convert "null dummy" to `null` value without reporting error.
+        if (str.toLowerCase().startsWith("null") && str != "null") {
+          JsonNodeFactory.instance.textNode(str)
+        } else {
+          MAPPER.readTree(str)
+        }
       } catch {
         case _: Exception => JsonNodeFactory.instance.textNode(str)
       }

src/test/scala/com/snowflake/snowpark_test/DataTypeSuite.scala

@@ -3,6 +3,7 @@ package com.snowflake.snowpark_test
 import com.snowflake.snowpark.{Row, SNTestBase, TestUtils}
 import com.snowflake.snowpark.types._
 import com.snowflake.snowpark.functions._
+import com.snowflake.snowpark.internal.Utils
 
 import java.sql.{Date, Time, Timestamp}
 import java.util.TimeZone
@@ -588,4 +589,28 @@ class DataTypeSuite extends SNTestBase {
            |""".stripMargin)
     // scalastyle:on
   }
+
+  test("Variant containing word null in the text")  {
+    import session.implicits._
+    var variant = new Variant("null string starts with null")
+    var df = Seq(variant).toDF("a")
+    checkAnswer(
+      df,
+      Row("\"null string starts with null\"")
+    )
+
+    variant = new Variant("string with null in the middle")
+    df = Seq(variant).toDF("a")
+    checkAnswer(
+      df,
+      Row("\"string with null in the middle\"")
+    )
+
+    variant = new Variant("string with null in the end null")
+    df = Seq(variant).toDF("a")
+    checkAnswer(
+      df,
+      Row("\"string with null in the end null\"")
+    )
+  }
 }