diff --git a/src/json/index.test.ts b/src/json/index.test.ts
index 3e96d7639..825bbc0e7 100644
--- a/src/json/index.test.ts
+++ b/src/json/index.test.ts
@@ -10,8 +10,8 @@ const testSchema = {
   requiredKey: json.string,
 };
 
-const optionalOrNullSchema = {
-  optionalKey: json.optionalOrNull(json.string),
+const optionalSchema = {
+  optionalKey: json.optional(json.string),
 };
 
 test("validateSchema - required properties are required", async (t) => {
@@ -30,34 +30,11 @@ test("validateSchema - required properties are required", async (t) => {
 
 test("validateSchema - optional properties are optional", async (t) => {
   // Optional fields may be absent
-  t.true(json.validateSchema(optionalOrNullSchema, {}));
-  t.true(json.validateSchema(optionalOrNullSchema, { optionalKey: undefined }));
-  t.true(json.validateSchema(optionalOrNullSchema, { optionalKey: null }));
-
-  // But, if present, should have the expected type
-  t.false(json.validateSchema(optionalOrNullSchema, { optionalKey: 0 }));
-  t.false(json.validateSchema(optionalOrNullSchema, { optionalKey: 123 }));
-  t.false(json.validateSchema(optionalOrNullSchema, { optionalKey: false }));
-  t.false(json.validateSchema(optionalOrNullSchema, { optionalKey: true }));
-  t.false(json.validateSchema(optionalOrNullSchema, { optionalKey: [] }));
-  t.false(json.validateSchema(optionalOrNullSchema, { optionalKey: {} }));
-  t.true(json.validateSchema(optionalOrNullSchema, { optionalKey: "" }));
-  t.true(json.validateSchema(optionalOrNullSchema, { optionalKey: "foo" }));
-});
-
-const optionalSchema = {
-  optionalKey: json.optional(json.string),
-};
-
-test("validateSchema - optional properties may be absent or undefined, but reject null", async (t) => {
-  // Optional fields may be absent or explicitly undefined
   t.true(json.validateSchema(optionalSchema, {}));
   t.true(json.validateSchema(optionalSchema, { optionalKey: undefined }));
+  t.true(json.validateSchema(optionalSchema, { optionalKey: null }));
 
-  // But should reject null
-  t.false(json.validateSchema(optionalSchema, { optionalKey: null }));
-
-  // And, if present, should have the expected type
+  // But, if present, should have the expected type
   t.false(json.validateSchema(optionalSchema, { optionalKey: 0 }));
   t.false(json.validateSchema(optionalSchema, { optionalKey: 123 }));
   t.false(json.validateSchema(optionalSchema, { optionalKey: false }));
diff --git a/src/json/index.ts b/src/json/index.ts
index 66adc606b..8a1b60a17 100644
--- a/src/json/index.ts
+++ b/src/json/index.ts
@@ -30,11 +30,6 @@ export function isString(value: unknown): value is string {
   return typeof value === "string";
 }
 
-/** Asserts that `value` is a number. */
-export function isNumber(value: unknown): value is number {
-  return typeof value === "number";
-}
-
 /** Asserts that `value` is either a string or undefined. */
 export function isStringOrUndefined(
   value: unknown,
@@ -60,23 +55,8 @@ export const string = {
   required: true,
 } as const satisfies Validator<string>;
 
-/** A validator for number fields in schemas. */
-export const number = {
-  validate: isNumber,
-  required: true,
-} as const satisfies Validator<number>;
-
-/** A validator for object fields in schemas. */
-export const object = {
-  validate: isObject,
-  required: true,
-} as const satisfies Validator<UnvalidatedObject<unknown>>;
-
-/**
- * Transforms a validator to be optional, accepting `undefined` or `null` for an
- * absent value.
- */
-export function optionalOrNull<T>(validator: Validator<T>) {
+/** Transforms a validator to be optional. */
+export function optional<T>(validator: Validator<T>) {
   return {
     validate: (val: unknown) => {
       return val === undefined || val === null || validator.validate(val);
@@ -85,19 +65,6 @@ export function optionalOrNull<T>(validator: Validator<T>) {
   } as const satisfies Validator<T | undefined | null>;
 }
 
-/**
- * Transforms a validator to be optional, accepting `undefined` for an absent
- * value but, unlike `optionalOrNull`, rejecting `null`.
- */
-export function optional<T>(validator: Validator<T>) {
-  return {
-    validate: (val: unknown): val is T | undefined => {
-      return val === undefined || validator.validate(val);
-    },
-    required: false,
-  } as const satisfies Validator<T | undefined>;
-}
-
 /** Represents an arbitrary object schema. */
 export type Schema = Record<string, Validator<any>>;
 
diff --git a/src/start-proxy/types.ts b/src/start-proxy/types.ts
index 13369edbf..13a4ce0e8 100644
--- a/src/start-proxy/types.ts
+++ b/src/start-proxy/types.ts
@@ -12,7 +12,7 @@ export type RawCredential = UnvalidatedObject<Credential>;
 /** A schema for credential objects with a username. */
 export const usernameSchema = {
   /** The username needed to authenticate to the package registry, if any. */
-  username: json.optionalOrNull(json.string),
+  username: json.optional(json.string),
 } as const satisfies json.Schema;
 
 /** Usernames may be present for both authentication with tokens or passwords. */
@@ -29,7 +29,7 @@ export function hasUsername(config: AuthConfig): config is Username {
 /** A schema for credential objects with a username and password. */
 export const usernamePasswordSchema = {
   /** The password needed to authenticate to the package registry, if any. */
-  password: json.optionalOrNull(json.string),
+  password: json.optional(json.string),
   ...usernameSchema,
 } as const satisfies json.Schema;
 
@@ -52,7 +52,7 @@ export function hasUsernameAndPassword(
 /** A schema for credential objects for token-based authentication. */
 export const tokenSchema = {
   /** The token needed to authenticate to the package registry, if any. */
-  token: json.optionalOrNull(json.string),
+  token: json.optional(json.string),
   ...usernameSchema,
 } as const satisfies json.Schema;
 
@@ -100,7 +100,7 @@ export const awsConfigSchema = {
   "role-name": json.string,
   domain: json.string,
   "domain-owner": json.string,
-  audience: json.optionalOrNull(json.string),
+  audience: json.optional(json.string),
 } as const satisfies json.Schema;
 
 /** Configuration for AWS OIDC. */
@@ -116,8 +116,8 @@ export function isAWSConfig(
 /** A schema for JFrog OIDC configurations. */
 export const jfrogConfigSchema = {
   "jfrog-oidc-provider-name": json.string,
-  audience: json.optionalOrNull(json.string),
-  "identity-mapping-name": json.optionalOrNull(json.string),
+  audience: json.optional(json.string),
+  "identity-mapping-name": json.optional(json.string),
 } as const satisfies json.Schema;
 
 /** Configuration for JFrog OIDC. */
@@ -150,8 +150,8 @@ export function isCloudsmithConfig(
 /** A schema for GCP OIDC configurations. */
 export const gcpConfigSchema = {
   "workload-identity-provider": json.string,
-  "service-account": json.optionalOrNull(json.string),
-  audience: json.optionalOrNull(json.string),
+  "service-account": json.optional(json.string),
+  audience: json.optional(json.string),
 } as const satisfies json.Schema;
 
 /** Configuration for GCP OIDC. */