Fix case expression (#2819)

src/common/expression/CaseExpression.cpp

@@ -64,10 +64,10 @@ const Value& CaseExpression::eval(ExpressionContext& ctx) {
  return result_;
  }
  } else {
- if (!when.isBool()) {
+ if (!when.isBool() && !when.isNull()) {
  return Value::kNullBadType;
  }
- if (when.getBool()) {
+ if (when.isBool() && when.getBool()) {
  result_ = whenThen.then->eval(ctx);
  return result_;
  }

tests/tck/features/aggregate/Agg.feature

@@ -11,6 +11,13 @@ Feature: Basic Aggregate and GroupBy
  Then the result should be, in any order, with relax comparison:
  | COUNT(*) | (1+1) |
  | 1 | 2 |
+ When executing query:
+ """
+ YIELD COUNT(CASE WHEN null THEN null ELSE 1 END) AS nulls
+ """
+ Then the result should be, in any order, with relax comparison:
+ | nulls |
+ | 1 |
  When executing query:
  """
  YIELD COUNT(*)+1 ,1+2 ,(INT)abs(count(2))

tests/tck/features/expression/Case.feature

@@ -36,6 +36,13 @@ Feature: Case Expression
  Then the result should be, in any order:
  | r |
  | 1 |
+ When executing query:
+ """
+ YIELD CASE WHEN null THEN 0 ELSE 1 END AS r
+ """
+ Then the result should be, in any order:
+ | r |
+ | 1 |
 
  Scenario: yield conditional case
  When executing query: