diff --git a/.eslintrc.js b/.eslintrc.js
index 04e9655d..92e65f3e 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -31,6 +31,7 @@ module.exports = {
     'no-multiple-empty-lines': 'error',
     'lines-between-class-members': 'off',
     '@typescript-eslint/lines-between-class-members': ['error', 'always', { exceptAfterSingleLine: true, exceptAfterOverload: true }],
+    '@typescript-eslint/no-empty-function': 'off',
   },
   settings: {
     'import/parsers': {
diff --git a/src/client/query/providers.ts b/src/client/query/providers.ts
index ad938483..af84c800 100644
--- a/src/client/query/providers.ts
+++ b/src/client/query/providers.ts
@@ -4,7 +4,6 @@ import {
   ProfileDocumentNode,
 } from '@superfaceai/ast';
 
-import { UnexpectedError } from '../../internal/errors';
 import {
   MapInterpreter,
   ProfileParameterValidator,
@@ -14,9 +13,7 @@ import { err, ok, Result } from '../../lib';
 import { Config } from '../config';
 import { fetchMapAST } from './registry';
 
-function forceCast<T>(_: unknown): _ is T {
-  return true;
-}
+function forceCast<T>(_: unknown): asserts _ is T {}
 
 export class BoundProvider {
   private profileValidator: ProfileParameterValidator;
@@ -25,8 +22,7 @@ export class BoundProvider {
     private profileAST: ProfileDocumentNode,
     private mapAST: MapDocumentNode,
     private config: Config,
-    // private usecase: string,
-    private baseUrl?: string // private validationFunction: (input: unknown) => input is TResult = isUnknown
+    private baseUrl?: string
   ) {
     this.profileValidator = new ProfileParameterValidator(this.profileAST);
   }
@@ -34,10 +30,10 @@ export class BoundProvider {
   /**
     Performs the usecase
   */
-  async perform<TInput extends NonPrimitive, TResult = unknown>(
-    input: TInput,
-    usecase: string
-  ): Promise<Result<TResult, unknown>> {
+  async perform<
+    TInput extends NonPrimitive | undefined = undefined,
+    TResult = unknown
+  >(usecase: string, input?: TInput): Promise<Result<TResult, unknown>> {
     const inputValidation = this.profileValidator.validate(
       input,
       'input',
@@ -71,15 +67,9 @@ export class BoundProvider {
       return err(resultValidation.error);
     }
 
-    if (forceCast<TResult>(result.value)) {
-      return ok(result.value);
-    }
+    forceCast<TResult>(result.value);
 
-    return err(
-      new UnexpectedError(
-        'This should be unreachable; how did you reach it? Are you magic?'
-      )
-    );
+    return ok(result.value);
   }
 
   public get serviceId(): string | undefined {
diff --git a/src/internal/errors.ts b/src/internal/errors.ts
index c72ef154..8d43d9db 100644
--- a/src/internal/errors.ts
+++ b/src/internal/errors.ts
@@ -3,7 +3,7 @@ export class ErrorBase {
 }
 
 export class UnexpectedError extends ErrorBase {
-  constructor(public message: string) {
+  constructor(public message: string, public additionalContext?: unknown) {
     super('UnexpectedError', message);
   }
 }
diff --git a/src/internal/interpreter/map-interpreter.ts b/src/internal/interpreter/map-interpreter.ts
index 4466e5ed..b06fb366 100644
--- a/src/internal/interpreter/map-interpreter.ts
+++ b/src/internal/interpreter/map-interpreter.ts
@@ -55,7 +55,9 @@ function assertUnreachable(node: MapASTNode): never {
   throw new UnexpectedError(`Invalid Node kind: ${node.kind}`);
 }
 
-export interface MapParameters<TInput extends NonPrimitive> {
+export interface MapParameters<
+  TInput extends NonPrimitive | undefined = undefined
+> {
   usecase?: string;
   auth?: Config['auth'];
   baseUrl?: string;
@@ -93,7 +95,8 @@ interface Stack {
   error?: MapInterpreterError;
 }
 
-export class MapInterpreter<TInput extends NonPrimitive> implements MapVisitor {
+export class MapInterpreter<TInput extends NonPrimitive | undefined>
+  implements MapVisitor {
   private operations: Record<string, OperationDefinitionNode | undefined> = {};
   private stack: Stack[] = [];
   private ast?: MapDocumentNode;
diff --git a/src/internal/interpreter/profile-parameter-validator.errors.ts b/src/internal/interpreter/profile-parameter-validator.errors.ts
index b791fc85..d516f1e9 100644
--- a/src/internal/interpreter/profile-parameter-validator.errors.ts
+++ b/src/internal/interpreter/profile-parameter-validator.errors.ts
@@ -76,6 +76,9 @@ export function formatErrors(errors?: ValidationError[]): string {
         case 'enumValue':
           return `${prefix}Invalid enum value`;
 
+        case 'wrongInput':
+          return `Wrong input`;
+
         default:
           throw new Error('Invalid error!');
       }
diff --git a/src/internal/interpreter/profile-parameter-validator.ts b/src/internal/interpreter/profile-parameter-validator.ts
index 86c89c28..770544bd 100644
--- a/src/internal/interpreter/profile-parameter-validator.ts
+++ b/src/internal/interpreter/profile-parameter-validator.ts
@@ -19,6 +19,7 @@ import {
 import createDebug from 'debug';
 
 import { err, ok, Result } from '../../lib';
+import { UnexpectedError } from '../errors';
 import { ProfileVisitor } from './interfaces';
 import {
   addFieldToErrors,
@@ -96,17 +97,21 @@ export class ProfileParameterValidator implements ProfileVisitor {
     kind: ProfileParameterKind,
     usecase: string
   ): Result<undefined, ProfileParameterError> {
-    const validator = this.visit(this.ast, kind, usecase);
-    const [result, errors] = validator(input);
+    try {
+      const validator = this.visit(this.ast, kind, usecase);
+      const [result, errors] = validator(input);
 
-    if (result !== true) {
-      const error =
-        kind === 'input' ? InputValidationError : ResultValidationError;
+      if (result !== true) {
+        const error =
+          kind === 'input' ? InputValidationError : ResultValidationError;
 
-      return err(new error(errors));
-    }
+        return err(new error(errors));
+      }
 
-    return ok(undefined);
+      return ok(undefined);
+    } catch (e) {
+      return err(new UnexpectedError('Unknown error from validator', e));
+    }
   }
 
   visit(
@@ -515,7 +520,7 @@ export class ProfileParameterValidator implements ProfileVisitor {
 
     return (input: unknown): ValidationResult => {
       if (
-        typeof input === undefined ||
+        typeof input === 'undefined' ||
         (typeof input === 'object' &&
           (input === null || Object.keys(input).length === 0))
       ) {