fix(workers-utils): reject null observability config instead of crashing

.changeset/observability-null-validation.md

@@ -0,0 +1,7 @@
+---
+"@cloudflare/workers-utils": patch
+---
+
+Return a clear error when `observability` is set to `null`
+
+`validateObservability` guarded only against `undefined`, so a `null` value (valid in JSON/JSONC config) passed the `typeof value === "object"` check and then threw `TypeError: Cannot read properties of null (reading 'enabled')` while validating the config. It now rejects `null` with the same `"observability" should be an object but got null.` diagnostic that the sibling `cache` validator already produces.

packages/workers-utils/src/config/validation.ts

@@ -6184,7 +6184,7 @@ const validateObservability: ValidatorFn = (diagnostics, field, value) => {
 		return true;
 	}
 
-	if (typeof value !== "object") {
+	if (typeof value !== "object" || value === null) {
 		diagnostics.errors.push(
 			`"${field}" should be an object but got ${JSON.stringify(value)}.`
 		);

packages/workers-utils/tests/config/validation/normalize-and-validate-config.test.ts

@@ -9828,6 +9828,22 @@ describe("normalizeAndValidateConfig()", () => {
 				`);
 			});
 
+			it("should error if observability is null", ({ expect }) => {
+				const { diagnostics } = normalizeAndValidateConfig(
+					{ observability: null } as unknown as RawConfig,
+					undefined,
+					undefined,
+					{ env: undefined }
+				);
+
+				expect(diagnostics.hasWarnings()).toBe(false);
+				expect(diagnostics.hasErrors()).toBe(true);
+				expect(diagnostics.renderErrors()).toMatchInlineSnapshot(`
+					"Processing wrangler configuration:
+					  - "observability" should be an object but got null."
+				`);
+			});
+
 			it("should not warn on full observability config", ({ expect }) => {
 				const { diagnostics } = normalizeAndValidateConfig(
 					{