Error validating event: 'm.relates_to' is a required property

Failed validating 'required' in schema['properties']['content']:
    {'type': 'object',
     'properties': {'m.relates_to': {'type': 'object',
                                     'properties': {'rel_type': {'type': 'string',
                                                                 'const': 'm.annotation'},
                                                    'event_id': {'type': 'string'},
                                                    'key': {'type': 'string'}},
                                     'required': ['rel_type',
                                                  'event_id',
                                                  'key']}},
     'required': ['m.relates_to']}

On instance['content']:
    {}
Error validating event: 'm.relates_to' is a required property

Failed validating 'required' in schema['properties']['content']:
    {'type': 'object',
     'properties': {'m.relates_to': {'type': 'object',
                                     'properties': {'rel_type': {'type': 'string',
                                                                 'const': 'm.annotation'},
                                                    'event_id': {'type': 'string'},
                                                    'key': {'type': 'string'}},
                                     'required': ['rel_type',
                                                  'event_id',
                                                  'key']}},
     'required': ['m.relates_to']}

On instance['content']:
    {}
Error validating event: 'm.relates_to' is a required property

Failed validating 'required' in schema['properties']['content']:
    {'type': 'object',
     'properties': {'m.relates_to': {'type': 'object',
                                     'properties': {'rel_type': {'type': 'string',
                                                                 'const': 'm.annotation'},
                                                    'event_id': {'type': 'string'},
                                                    'key': {'type': 'string'}},
                                     'required': ['rel_type',
                                                  'event_id',
                                                  'key']}},
     'required': ['m.relates_to']}

On instance['content']:
    {}
Error validating event: 'm.relates_to' is a required property

Failed validating 'required' in schema['properties']['content']:
    {'type': 'object',
     'properties': {'m.relates_to': {'type': 'object',
                                     'properties': {'rel_type': {'type': 'string',
                                                                 'const': 'm.annotation'},
                                                    'event_id': {'type': 'string'},
                                                    'key': {'type': 'string'}},
                                     'required': ['rel_type',
                                                  'event_id',
                                                  'key']}},
     'required': ['m.relates_to']}

On instance['content']:
    {}