Fix a panic during diff

provider/pkg/provider/diff_test.go

@@ -15,9 +15,11 @@ import (
 	"k8s.io/apimachinery/pkg/runtime/schema"
 )
 
-type object = map[string]any
-type list = []any
-type expected = map[string]*pulumirpc.PropertyDiff
+type (
+	object   = map[string]any
+	list     = []any
+	expected = map[string]*pulumirpc.PropertyDiff
+)
 
 func TestPatchToDiff(t *testing.T) {
 	var (
@@ -232,6 +234,15 @@ func TestPatchToDiff(t *testing.T) {
 				"spec.containers[0]": U,
 			},
 		},
+		{
+			name:  "Removing a field that was nil should not panic (#1970).",
+			group: "tekton.dev", version: "v1beta1", kind: "Pipeline",
+			old: object{"taskSpec": object{"spec": nil, "steps": list{object{"name": "something"}}}},
+			new: object{"taskSpec": object{"steps": list{object{"name": "something-else"}}}},
+			expected: expected{
+				"taskSpec.steps[0].name": U,
+			},
+		},
 	}
 
 	for _, tt := range tests {

provider/pkg/provider/provider.go

@@ -3017,12 +3017,12 @@ type patchConverter struct {
 	diff     map[string]*pulumirpc.PropertyDiff
 }
 
-// addPatchValueToDiff adds the given patched value to the detailed diff. Either the patched value or the old value
-// must not be nil.
+// addPatchValueToDiff adds the given patched value to the detailed diff.
 //
 // The particular difference that is recorded depends on the old and new values:
 // - If the patched value is nil, the property is recorded as deleted
 // - If the old value is nil, the property is recorded as added
+// - If the old and patched values are both nil, no diff is recorded.
 // - If the types of the old and new values differ, the property is recorded as updated
 // - If both values are maps, the maps are recursively compared on a per-property basis and added to the diff
 // - If both values are arrays, the arrays are recursively compared on a per-element basis and added to the diff
@@ -3035,9 +3035,9 @@ type patchConverter struct {
 func (pc *patchConverter) addPatchValueToDiff(
 	path []any, v, old, newInput, oldInput any, inArray bool,
 ) error {
-	contract.Assertf(v != nil || old != nil || oldInput != nil || newInput != nil,
-		"path: %+v  |  v: %+v  | old: %+v  |  oldInput: %+v  |  newInput: %+v",
-		path, v, old, oldInput, newInput)
+	if v == nil && old == nil && oldInput == nil && newInput == nil {
+		return nil
+	}
 
 	// If there is no new input, then the only possible diff here is a delete. All other diffs must be diffs between
 	// old and new properties that are populated by the server. If there is also no old input, then there is no diff