[Fix](Planner) fix case function with null cast to array null (#22947)

fe/fe-core/src/main/java/org/apache/doris/analysis/CastExpr.java

@@ -314,7 +314,7 @@ public void analyze() throws AnalysisException {
         // it is necessary to check if it is castable before creating fn.
         // char type will fail in canCastTo, so for compatibility, only the cast of array type is checked here.
         if (type.isArrayType() || childType.isArrayType()) {
-            if (childType.isNull() || !Type.canCastTo(childType, type)) {
+            if (!Type.canCastTo(childType, type)) {
                 throw new AnalysisException("Invalid type cast of " + getChild(0).toSql()
                         + " from " + childType + " to " + type);
             }

regression-test/data/query_p0/sql_functions/case_function/test_case_function_null.out

@@ -16,3 +16,6 @@
 -- !sql_case2 --
 -2
 
+-- !sql_case3 --
+0
+

regression-test/data/query_p0/sql_functions/cast_function/test_cast_array_functions_by_literal.out

@@ -23,3 +23,6 @@
 -- !sql8 --
 \N
 
+-- !sql9 --
+\N
+

regression-test/suites/query_p0/sql_functions/case_function/test_case_function_null.groovy

@@ -228,4 +228,8 @@ suite("test_case_function_null", "query,p0") {
             END)
         FROM case_null2;
     """
-}
+
+
+    qt_sql_case3 """SELECT COUNT(CASE (NOT (NOT true))  WHEN (((- 47960023)) IS NOT NULL) THEN NULL ELSE NULL END) from case_null1;"""
+
+}

regression-test/suites/query_p0/sql_functions/cast_function/test_cast_array_functions_by_literal.groovy

@@ -41,11 +41,7 @@ suite("test_cast_array_functions_by_literal") {
     // empty string is invalid array, return NULL
     qt_sql8 """select cast('' as array<string>)"""
 
-    test {
-        sql "select cast(NULL as array<int>)"
-        // check exception message contains
-        exception "errCode = 2,"
-    }
+    qt_sql9 """select cast(NULL as array<int>)"""
 
     test {
         sql "select cast(1 as array<int>)"