# Type of request: This is a ...

[X ] bug report
[ ] feature request

# Detailed description
Calling PutEvents operation returns 500 if no `Detail` is specified. This case is similar to #3043

## Expected behavior
According to the doc https://docs.aws.amazon.com/eventbridge/latest/APIReference/API_PutEventsRequestEntry.html `Details` is optional. 

```
 Detail
    A valid JSON string. There is no other schema imposed. The JSON string may contain fields and nested subobjects.
    Type: String
    Required: No
```

So this should works and set `Detail` as `{}`

```
eb_client = boto3.client('events', endpoint_url='http://localhost:4587')
eb_client.put_events(
    Entries=[
        {
            'DetailType': 'Test'
        }
    ]
)
```

## Actual behavior
500 is returned

# Steps to reproduce

1. Start LocalStack with SERVICES=events
2. Run the client code

## Command used to start LocalStack

```
docker run --rm --name localstack -p 4587:4587 -e SERVICES=events -e DEBUG=true localstack/localstack
```

## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)

CLI:

```
aws events put-events --endpoint-url http://localhost:4587 --entries '[{"DetailType": "Test"}]'
```

Or via python:

```
eb_client = boto3.client('events', endpoint_url='http://localhost:4587')
eb_client.put_events(
    Entries=[
        {
            'DetailType': 'Test',
            'Detail': '{}'
        }
    ]
)
```

event_value <= element_value[index + 1]:
                            break
                        elif element_value[index] == '>=' and \
                            isinstance(element_value[index + 1], int) and \
                                event_value < element_value[index + 1]:
                            break
                        elif element_value[index] == '<' and \
                            isinstance(element_value[index + 1], int) and \
                                event_value >= element_value[index + 1]:
                            break
                        elif element_value[index] == '<=' and \
                            isinstance(element_value[index + 1], int) and \
                                event_value > element_value[index + 1]:
                            break
                    else:
                        return True
            elif element_key.lower() == 'anything-but':
                if isinstance(element_value, list) and \
                        event_value not in element_value:
                    return True
                elif (isinstance(element_value, (str, int))) and \
                        event_value != element_value:
                    return True
                elif isinstance(element_value, dict):
                    nested_key = list(element_value)[0]
                    if nested_key == 'prefix' and \
                            not re.match(r'^{}'.format(element_value.get(nested_key)), event_value):
                        return True
    return False
def check_valid_numeric_content_base_rule(list_of_operators):