'Retrieves the output mask tensor(s) of a layer.
Only applicable if the layer has exactly one inbound node,
i.e. if it is connected to one incoming layer.
# Returns
Output mask tensor (potentially None) or list of output
mask tensors.
# Raises
AttributeError: if the layer is connected to
more than one incoming layers.'

@property
def output_mask(self):

    if (len(self.inbound_nodes) != 1):
        raise AttributeError((('Layer    ' + self.name) + '    has    multiple    inbound    nodes,    hence    the    notion    of    "layer    output    mask"    is    ill-defined.    Use    `get_output_mask_at(node_index)`    instead.'))
    return self._get_node_attribute_at_index(0, 'output_masks', 'output    mask')
