React red warning -- need to research

[gbenavid]

line 46 in ShoppingList.js

      <section>
        {map(shoppingLists, (shoppingList, key) => (        
          <ShoppingList key={key} 
                        appendTo={key} 
                        user={user}
                        content={this.state.listedItems}
                        toggleItems={ () => this.toggleItems(key,shoppingList.name)}
                        handleDelete={ () => this.handleDelete(key)}
                        {...shoppingList}
          />
        ))}
      </section>