fix tests

Author: statictype

packages/api-contract/src/Abi/index.ts

@@ -110,7 +110,7 @@ export class Abi {
     );
     this.constructors = this.metadata.spec.constructors.map((spec: ContractConstructorSpecLatest, index) => {
       const isDefault = 'default' in spec ? spec.default.isTrue : undefined;
-      const typeSpec = spec.returnType.unwrapOr(null);
+      const typeSpec = '' in spec ? spec.returnType.unwrapOr(null) : null;
 
       return this.#createMessage(spec, index, {
         isConstructor: true,