I scanned the heavy whipping cream container and it shows up with net carbs even when the container shows zero?
Food labels do get updated over time, or it is also possible that the information wasn't correct when the user first submitted it (assuming it's a user-submitted food item). You should report the issue by right clicking on the heavy whipping cream entry, View/Edited Selected Food, gear icon near the top right and "Report Issue..."
It looks like there is a small amount of carbohydrates in Heavy Cream. Check out "Heavy Cream" from NCCDB or "Heavy Whipping Cream" from USDA. They list about 0.4 g total carbohydrates per 1 Tbsp (15 g)
When the nutrient values are low, manufacturers are permitted to round the value down to zero, if they like. So for brand name products, you may find that sometimes they may choose to round the value to 1, while others may choose to round the value to zero.
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If you use more than a tablespoon, it adds up to real carbs.