code: public static boolean isPlaceholderShape(int[] shape) {
          if(shape == null)
              return true;
          else {
              for(int i = 0; i < shape.length; i++) {
                  if(shape[i] < 0)
                      return true;
              }
          }
  
          return false;
      }
docs: Returns true if any shape has a -1
  or a null or empty array is passed in
  @param shape the input shape to validate
  @return true if the shape is null,empty, or contains a -1 element