d3m.primitives.clustering.kmeans_clustering.UBC primitive fails when receives only one column as inputs

[roquelopez]

Traceback (most recent call last):
  File "/src/d3m/d3m/runtime.py", line 1114, in _do_run_step
    self._run_step(step)
  File "/src/d3m/d3m/runtime.py", line 1104, in _run_step
    self._run_primitive(step)
  File "/src/d3m/d3m/runtime.py", line 979, in _run_primitive
    multi_call_result = self._call_primitive_method(primitive.fit_multi_produce, fit_multi_produce_arguments)
  File "/src/d3m/d3m/runtime.py", line 1080, in _call_primitive_method
    raise error
  File "/src/d3m/d3m/runtime.py", line 1076, in _call_primitive_method
    result = method(**arguments)
  File "/src/d3m/d3m/primitive_interfaces/unsupervised_learning.py", line 48, in fit_multi_produce
    return self._fit_multi_produce(produce_methods=produce_methods, timeout=timeout, iterations=iterations, inputs=inputs)
  File "/src/d3m/d3m/primitive_interfaces/base.py", line 570, in _fit_multi_produce
    produce_results = self._multi_produce(produce_methods=produce_methods, timeout=timeout, iterations=iterations, **kwargs)
  File "/src/d3m/d3m/primitive_interfaces/base.py", line 466, in _multi_produce
    results.append(getattr(self, method_name)(timeout=timeout, iterations=iterations, **arguments))
  File "/src/ubc-primitives/primitives_ubc/kmeans/kmeansClustering.py", line 263, in produce
    outputs = inputs.remove_columns(feature_columns)
  File "/src/d3m/d3m/container/pandas.py", line 256, in remove_columns
    raise ValueError("Removing columns would have removed the last column.")
ValueError: Removing columns would have removed the last column.