src/main/java/com/bazaarvoice/jackson/rison/RisonParser.java
protected JsonToken _handleUnexpectedValue(int i)
            throws IOException, JsonParseException
    {
        // Most likely an error, unless we are to allow single-quote-strings
        switch (i) {
            case 'N':
                _matchToken("NaN", 1);
                if (isEnabled(JsonParser.Feature.ALLOW_NON_NUMERIC_NUMBERS)) {
                    return resetAsNaN("NaN", Double.NaN);
                }
                _reportError("Non-standard token 'NaN': enable JsonParser.Feature.ALLOW_NON_NUMERIC_NUMBERS to allow");
                break;
            case '+': // note: '-' is taken as number
                if (_inputPtr >= _inputEnd) {
                    if (!loadMore()) {
                        _reportInvalidEOFInValue();
                    }
                }
                return _handleInvalidNumberStart(_inputBuffer[_inputPtr++], false);
        }
        _reportUnexpectedChar(i, "expected a valid value (number, String, array, object, 'true', 'false' or 'null')");
        return null;
    }
protected JsonToken _handleUnexpectedValue(int i)
            throws IOException, JsonParseException
    {
        // Most likely an error, unless we are to allow single-quote-strings
        switch (i) {
            case 'N':
                _matchToken("NaN", 1);
                if (isEnabled(JsonParser.Feature.ALLOW_NON_NUMERIC_NUMBERS)) {
                    return resetAsNaN("NaN", Double.NaN);
                }
                _reportError("Non-standard token 'NaN': enable JsonParser.Feature.ALLOW_NON_NUMERIC_NUMBERS to allow");
                break;
            case '+': // note: '-' is taken as number
                if (_inputPtr >= _inputEnd) {
                    if (!loadMore()) {
                        _reportInvalidEOFInValue();
                    }
                }
                return _handleInvalidNumberStart(_inputBuffer[_inputPtr++], false);
        }
        _reportUnexpectedChar(i, "expected a valid value (number, String, array, object, 'true', 'false' or 'null')");
        return null;
    }
Method for handling cases where first non-space character
of an expected value token is not legal for standard JSON content.