ValueError: need at least one array to concatenate about ssd_keras HOT 2 CLOSED

pred = np.concatenate(pred, axis=0)
if pred.shape[0] > top_k: # If we have more than `top_k` results left at this point, otherwise there is nothing to filter,...
top_k_indices = np.argpartition(pred[:,1], kth=pred.shape[0]-top_k, axis=0)[pred.shape[0]-top_k:] # ...get the indices of the `top_k` highest-score maxima...
pred = pred[top_k_indices] # ...and keep only those entries of `pred`...

if len(pred):
    pred = np.concatenate(pred, axis=0)
    if pred.shape[0] > top_k: # If we have more than `top_k` results left at this point, otherwise there is nothing to filter,...
        top_k_indices = np.argpartition(pred[:,1], kth=pred.shape[0]-top_k, axis=0)[pred.shape[0]-top_k:] # ...get the indices of the `top_k` highest-score maxima...
        pred = pred[top_k_indices] # ...and keep only those entries of `pred`...