Update new-dmn-check to make better null tests

Author: prestoncabe

.claude/commands/new-dmn-check.md

@@ -372,6 +372,21 @@ assert {
 
 Use a situation where the relevant field is absent or set to `null`, triggering the null-return branch of the FEEL expression.
 
+**simpleChecks-based checks**: when the check reads `situation.simpleChecks.<fieldName>`, the Null case must set the **specific boolean field** to `null` — not the entire `simpleChecks` object. This tests the inner null guard in the FEEL expression:
+```json
+"situation": {
+  "simpleChecks": {
+    "tenYearTaxAbatement": null
+  }
+}
+```
+Not:
+```json
+"situation": {
+  "simpleChecks": null
+}
+```
+
 **Parameterless checks**: omit `"parameters"` from the request body entirely in all three test files. Do not send `"parameters": {}` or `"parameters": null`.
 
 Use realistic test data: concrete IDs (e.g. `"p1"`), dates (ISO 8601), and parameter values that clearly demonstrate the pass vs. fail condition.
@@ -416,3 +431,4 @@ After writing all files, print:
 10. **Always import the category base module** — every check must import its category's base module DMN (e.g. `Residence.dmn`, `Age.dmn`), even if no types or BKMs from it are used in this check.
 11. **DMNDI: inputs below, no unused imported shapes** — input nodes must always be placed below the decision service box (higher y). Never add `DMNShape` entries for BKMs or elements from imported modules unless they are explicitly called by a `dmn:knowledgeRequirement` in this check.
 12. **Parameterless checks omit `parameters` entirely** — if the check has no caller-supplied parameters, remove `tParameters`, the `parameters` inputData element, its `dmn:informationRequirement`, its DMNDI shape and edge, and the `"parameters"` key from all Bruno test request bodies. An absent `parameters` input in the DMN type system is the correct way to express this; do not use an empty context or null type.
+13. **simpleChecks Null.bru targets the specific field** — when the check reads `situation.simpleChecks.<fieldName>`, the Null test must set that specific boolean field to `null`, not the entire `simpleChecks` object to `null`. Setting the parent object to null tests a different (shallower) branch of the FEEL null guard than is most useful.