presto-main/src/main/java/io/prestosql/sql/planner/TranslationMap.java/TranslationMap/get
class TranslationMap:    public Symbol get(Expression expression)
    {
        if (expression instanceof FieldReference) {
            int field = ((FieldReference) expression).getFieldIndex();
            checkArgument(fieldSymbols[field] != null, "No mapping for field: %s", field);
            return fieldSymbols[field];
        }

        Expression translated = translateNamesToSymbols(expression);
        if (!expressionToSymbols.containsKey(translated)) {
            checkArgument(expressionToExpressions.containsKey(translated), "No mapping for expression: %s", expression);
            return get(expressionToExpressions.get(translated));
        }

        return expressionToSymbols.get(translated);
    }