feat(ingredients): make units nullable

internal/processor/ingredient_unit_converter_processor.go

@@ -266,15 +266,27 @@ func (p *IngredientUnitConverterProcessorImpl) GetUnitsByIngredientID(ctx contex
 		return nil, fmt.Errorf("failed to get ingredient: %w", err)
 	}
 
-	// Get the base unit details
-	baseUnit, err := p.unitRepo.GetByID(ctx, ingredient.UnitID, organizationID)
-	if err != nil {
-		return nil, fmt.Errorf("failed to get base unit: %w", err)
+	response := &models.IngredientUnitsResponse{
+		IngredientID:   ingredientID,
+		IngredientName: ingredient.Name,
 	}
 
-	// Start with the base unit
-	units := []*models.UnitResponse{
-		mappers.MapUnitEntityToResponse(baseUnit),
+	units := make([]*models.UnitResponse, 0)
+	unitMap := make(map[uuid.UUID]bool)
+
+	// An ingredient does not necessarily have a unit assigned yet. When it has
+	// none there is no base unit to start from, so the only units on offer are
+	// the ones its converters mention.
+	if ingredient.UnitID != nil {
+		baseUnit, err := p.unitRepo.GetByID(ctx, *ingredient.UnitID, organizationID)
+		if err != nil {
+			return nil, fmt.Errorf("failed to get base unit: %w", err)
+		}
+
+		units = append(units, mappers.MapUnitEntityToResponse(baseUnit))
+		unitMap[baseUnit.ID] = true
+		response.BaseUnitID = &baseUnit.ID
+		response.BaseUnitName = baseUnit.Name
 	}
 
 	// Get all converters for this ingredient
@@ -283,10 +295,6 @@ func (p *IngredientUnitConverterProcessorImpl) GetUnitsByIngredientID(ctx contex
 		return nil, fmt.Errorf("failed to get converters: %w", err)
 	}
 
-	// Add unique units from converters
-	unitMap := make(map[uuid.UUID]bool)
-	unitMap[baseUnit.ID] = true
-
 	for _, converter := range converters {
 		if converter.IsActive {
 			// Add FromUnit if not already added
@@ -309,13 +317,7 @@ func (p *IngredientUnitConverterProcessorImpl) GetUnitsByIngredientID(ctx contex
 		}
 	}
 
-	response := &models.IngredientUnitsResponse{
-		IngredientID:   ingredientID,
-		IngredientName: ingredient.Name,
-		BaseUnitID:     baseUnit.ID,
-		BaseUnitName:   baseUnit.Name,
-		Units:          units,
-	}
+	response.Units = units
 
 	return response, nil
 }