SQL: Fix null handling for IN => painless script (#35124)

Include `null` literals when generating the painless script for `IN` expressions.
Previously, they were skipped, because of an issue that had been fixed with #35108.

Fixes: #35122

Author: Marios Trivyzas

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/expression/predicate/operator/comparison/In.java

@@ -107,9 +107,9 @@ public Attribute toAttribute() {
     @Override
     public ScriptTemplate asScript() {
         ScriptTemplate leftScript = asScript(value);
-        // remove duplicates
+
+        // fold & remove duplicates
         List<Object> values = new ArrayList<>(new LinkedHashSet<>(Foldables.valuesOf(list, value.dataType())));
-        values.removeIf(Objects::isNull);
 
         return new ScriptTemplate(
             formatTemplate(String.format(Locale.ROOT, "{sql}.in(%s, {})", leftScript.template())),
@@ -141,6 +141,6 @@ public boolean equals(Object obj) {
 
         In other = (In) obj;
         return Objects.equals(value, other.value)
-                && Objects.equals(list, other.list);
+            && Objects.equals(list, other.list);
     }
 }

x-pack/plugin/sql/src/test/java/org/elasticsearch/xpack/sql/planner/QueryTranslatorTests.java

@@ -213,7 +213,7 @@ public void testTranslateInExpression_WhereClause_Painless() {
         assertEquals("InternalSqlScriptUtils.nullSafeFilter(InternalSqlScriptUtils.in(" +
                 "InternalSqlScriptUtils.power(InternalSqlScriptUtils.docValue(doc,params.v0),params.v1), params.v2))",
             sc.script().toString());
-        assertEquals("[{v=int}, {v=2}, {v=[10.0, 20.0]}]", sc.script().params().toString());
+        assertEquals("[{v=int}, {v=2}, {v=[10.0, null, 20.0]}]", sc.script().params().toString());
     }
 
     public void testTranslateInExpression_HavingClause_Painless() {
@@ -259,6 +259,6 @@ public void testTranslateInExpression_HavingClause_PainlessAndNullHandling() {
         assertEquals("InternalSqlScriptUtils.nullSafeFilter(InternalSqlScriptUtils.in(params.a0, params.v0))",
             aggFilter.scriptTemplate().toString());
         assertThat(aggFilter.scriptTemplate().params().toString(), startsWith("[{a=MAX(int){a->"));
-        assertThat(aggFilter.scriptTemplate().params().toString(), endsWith(", {v=[10, 20, 30]}]"));
+        assertThat(aggFilter.scriptTemplate().params().toString(), endsWith(", {v=[10, null, 20, 30]}]"));
     }
 }