presto-main/src/main/java/io/prestosql/sql/analyzer/ExpressionAnalyzer.java/Visitor/visitBooleanLiteral
class Visitor:        @Override
        protected Type visitBooleanLiteral(BooleanLiteral node, StackableAstVisitorContext<Context> context)
        {
            return setExpressionType(node, BOOLEAN);
        }