Flutter DropDownMenu (RangeError (length): Invalid value: Valid value range is empty: 0)

I’m using a DropDownMenu in Flutter to search for items in my ProductList. As soon as I type something that wouldn’t match the value of a product in the list, I get this error: RangeError (length): Invalid value: Valid value range is empty: 0

Here’s the code that I tried:

      products.when(
      data: (productList) { 
      var filteredList = searchController.text.isNotEmpty ? productList
                                .where((e) => e.name.contains(RegExp(
                                    searchController.text,
                                    caseSensitive: false)))
                                .toList()
                            : productList.take(5).toList();

    return SizedBox(
                          child: DropdownMenu<String?>( 
                            textStyle: TextStyle(color: Colors.black),
                            inputDecorationTheme: InputDecorationTheme(
                              hintStyle: TextStyle(color: Colors.black),
                              helperStyle: TextStyle(color: Colors.black),
                              labelStyle: TextStyle(color: Colors.black),
                            ),
                            controller: searchController,
                            width: 350,
                            hintText: "Search for a product...",
                            requestFocusOnTap: true,
                            enableFilter: true,
                            enabled: selectedProduct == null,
                            label: const Text('Select A Product'),
                            onSelected: (String? selectedProductName) {
                              setState(() {
                                selectedProduct = selectedProductName;
                              });
                            },
                            dropdownMenuEntries: filteredList.isEmpty
                                ? [
                                    DropdownMenuEntry<String?>(
                                      value: '',
                                      label: 'No results found.',
                                    )
                                  ]
                                : filteredList.map<DropdownMenuEntry<String?>>(
                                    (ProductModel product) {
                                    return DropdownMenuEntry<String?>(
                                      value: product.id.toString(),
                                      label:
                                          '${product.name} (${product.location})',
                                    );
                                  }).toList(),
                          ),
                        );
                      },
                      error: (_, __) => getLoadError(_),
                      loading: () => getLoadIndicator(),
                    ),

My productList loads fine.

EDIT: This error only occurs if the filteredList was populated by the search initially. If I search for something that doesn’t exist initially, it wouldn’t give me this error..
For example, if this list contains [Apples, Oranges] and I search "OA" I get the error, but if I search "Zzz", it gives me the empty list.