# Buggy code
def __init__(self, storage_writer, path):
    """Initializes a storage merge reader.

    Args:
      storage_writer (StorageWriter): storage writer.
      path (str): path to the input file.

    Raises:
      IOError: if the input file cannot be opened.
      RuntimeError: if an add container method is missing.
    """
    super(SQLiteStorageMergeReader, self).__init__(storage_writer)
    self._active_container_type = None
    self._active_cursor = None
    self._add_active_container_method = None
    self._add_container_type_methods = {}
    self._compression_format = definitions.COMPRESSION_FORMAT_NONE
    self._connection = None
    self._container_types = None
    self._cursor = None
    self._event_data_identifier_mappings = {}
    self._path = path

    # Create a runtime lookup table for the add container type method. This
    # prevents having to create a series of if-else checks for container types.
    # The table is generated at runtime as there are no forward function
    # declarations in Python.
    for container_type, method_name in self._ADD_CONTAINER_TYPE_METHODS.items():
        method = getattr(self, method_name, None)
        if not method:
            raise RuntimeError(
                "Add method missing for container type: {0:s}".format(container_type)
            )

        self._add_container_type_methods[container_type] = method


# Traceback (ValueError)
Traceback (most recent call last):
File "plaso/tools/log2timeline.py", line 97, in <module>
if not Main():
File "plaso/tools/log2timeline.py", line 72, in Main
tool.ExtractEventsFromSources()
File "plaso/plaso/cli/log2timeline_tool.py", line 448, in ExtractEventsFromSources
worker_memory_limit=self._worker_memory_limit)
File "plaso/plaso/multi_processing/task_engine.py", line 812, in ProcessSources
self._ProcessSources(source_path_specs, storage_writer)
File "plaso/plaso/multi_processing/task_engine.py", line 343, in _ProcessSources
self._ScheduleTasks(storage_writer)
File "plaso/plaso/multi_processing/task_engine.py", line 449, in _ScheduleTasks
self._MergeTaskStorage(storage_writer)
File "plaso/plaso/multi_processing/task_engine.py", line 256, in _MergeTaskStorage
maximum_number_of_containers=self._MAXIMUM_NUMBER_OF_CONTAINERS)
File "plaso/plaso/storage/sqlite/merge_reader.py", line 278, in MergeAttributeContainers
self._active_container_type, serialized_data)
File "plaso/plaso/storage/interface.py", line 600, in _DeserializeAttributeContainer
attribute_container = self._serializer.ReadSerialized(serialized_string)
File "plaso/plaso/serializer/json_serializer.py", line 404, in ReadSerialized
return cls.ReadSerializedDict(json_dict)
File "plaso/plaso/serializer/json_serializer.py", line 423, in ReadSerializedDict
json_object = cls._ConvertDictToObject(json_dict)
File "plaso/plaso/serializer/json_serializer.py", line 252, in _ConvertDictToObject
'supported.').format(attribute_name))
ValueError: Event data attribute value: return_value of type dict is not supported.

# Fixed code
def __init__(self, storage_writer, path):
    """Initializes a storage merge reader.

    Args:
      storage_writer (StorageWriter): storage writer.
      path (str): path to the input file.

    Raises:
      IOError: if the input file cannot be opened.
      RuntimeError: if an add container method is missing.
    """
    super(SQLiteStorageMergeReader, self).__init__(storage_writer)
    self._active_container_type = None
    self._active_cursor = None
    self._add_active_container_method = None
    self._add_container_type_methods = {}
    self._compression_format = definitions.COMPRESSION_FORMAT_NONE
    self._connection = None
    self._container_types = None
    self._cursor = None
    self._deserialization_errors = []
    self._event_data_identifier_mappings = {}
    self._path = path

    # Create a runtime lookup table for the add container type method. This
    # prevents having to create a series of if-else checks for container types.
    # The table is generated at runtime as there are no forward function
    # declarations in Python.
    for container_type, method_name in self._ADD_CONTAINER_TYPE_METHODS.items():
        method = getattr(self, method_name, None)
        if not method:
            raise RuntimeError(
                "Add method missing for container type: {0:s}".format(container_type)
            )

        self._add_container_type_methods[container_type] = method