NdArray implementations don't throw IllegalRankException as documented if no coordinates provided

Instead, when no coordinates are provided, we return the scalar at (0, 0, ...). Is this an important idiom that we are preserving, or a questionable choice, or simply a bug?

Here's an example of an abstract method of FloatNdArray that is documented to throw IllegalRankException:

 /**
   * Returns the float value of the scalar found at the given coordinates.
   *
   * . . .
   *
   * @param coordinates coordinates of the scalar to resolve
   * @return value of that scalar
   * @throws IndexOutOfBoundsException if some coordinates are outside the limits of their respective dimension
   * @throws IllegalRankException if number of coordinates is not sufficient to access a scalar element
   */
  float getFloat(long... coordinates);

Here's the implementation in FloatDenseNdArray:

  @Override
  public float getFloat(long... indices) {
    return buffer.getFloat(positionOf(indices, true));
  }

But if indices.length == 0, then positionOf does not throw the claimed IllegalRankException:

  long positionOf(long[] coords, boolean isValue) {
    if (coords == null || coords.length == 0) {
      return 0;
    }
    Validator.coordinates(dimensions, coords, isValue);
    return dimensions.positionOf(coords);
  }

Start with the documented FloatNdArray.getFloat contract and compare it with FloatDenseNdArray.getFloat and positionOf, especially the zero-coordinate branch. Determine whether returning the scalar at position 0 is intended or violates the documented exception behavior; done means the behavior and its documentation agree, with relevant coverage added or updated if the project provides it.