Add defensive checks and tests for single-array JSON spatial query responses

fdm-calculator/src/norms/nl/2025/dierlijke-mest-gebruiksnorm.test.ts

@@ -79,4 +79,19 @@ describe("getNL2025DierlijkeMestGebruiksNorm", () => {
             "Derogatie - Grondwaterbeschermingsgebied",
         )
     })
+
+    it("should return the default norm value for derogation outside Grondwaterbeschermingsgebied and inside NV-gebied, but with single array response (see #205)", async () => {
+        const mockInput: NL2025NormsInput = {
+            farm: { is_derogatie_bedrijf: true },
+            field: {
+                b_id: "1",
+                b_centroid: [5.058131582583726, 52.50733333508596],
+            },
+            cultivations: [],
+            soilAnalysis: { a_p_cc: 0, a_p_al: 0 },
+        }
+        const result = await getNL2025DierlijkeMestGebruiksNorm(mockInput)
+        expect(result.normValue).toBe(190)
+        expect(result.normSource).toBe("Derogatie - NV Gebied")
+    })
 })

fdm-calculator/src/norms/nl/2025/dierlijke-mest-gebruiksnorm.ts

@@ -32,9 +32,11 @@ export async function isFieldInGWGBGebied(
             throw new Error(`Failed to fetch ${url}: ${response.statusText}`)
         }
         const json = await response.json()
-        const feature = json[0][0]
-        if (feature) {
-            return true
+        if (json.length > 0) { // Check if not single array response
+            const feature = json[0][0]
+            if (feature) {
+                return true
+            }
         }
         return false
     } catch (err) {

fdm-calculator/src/norms/nl/2025/stikstofgebruiksnorm.test.ts

@@ -21,6 +21,12 @@ describe("stikstofgebruiksnorm helpers", () => {
         expect(result).toBe(false)
     })
 
+    it("should correctly identify a field not in an NV Gebied, but with single array response (see #205)", async () => {
+        const centroidOutsideNV = [5.5527872994244785, 52.92595151470198] // Known point outside NV Gebied
+        const result = await isFieldInNVGebied(centroidOutsideNV)
+        expect(result).toBe(false)
+    })
+
     it("should correctly identify the region for a field", async () => {
         const centroidInKlei = [5.64188724, 51.977587] // Known point in Klei
         const region = await getRegion(centroidInKlei)

fdm-calculator/src/norms/nl/2025/stikstofgebruiksnorm.ts

@@ -38,9 +38,12 @@ export async function isFieldInNVGebied(
             throw new Error(`Failed to fetch ${url}: ${response.statusText}`)
         }
         const json = await response.json()
-        const feature = json[0][0]
-        if (feature) {
-            return true
+        if (json.length > 0) {
+            // Check if not single array response
+            const feature = json[0][0]
+            if (feature) {
+                return true
+            }
         }
         return false
     } catch (err) {