presto-main/src/main/java/io/prestosql/sql/planner/ExpressionInterpreter.java/ExpressionInterpreter/getValue
class ExpressionInterpreter:        @Override
        public Object getValue(Symbol symbol)
        {
            checkState(values.containsKey(symbol.getName()), "values does not contain %s", symbol);
            return values.get(symbol.getName());
        }