presto-main/src/main/java/io/prestosql/sql/analyzer/ExpressionAnalyzer.java/ExpressionAnalyzer/visitCharLiteral
class ExpressionAnalyzer:        @Override
        protected Type visitCharLiteral(CharLiteral node, StackableAstVisitorContext<Context> context)
        {
            CharType type = CharType.createCharType(node.getValue().length());
            return setExpressionType(node, type);
        }