Merge pull request #1543 from 0xProject/fix/asset-buyer-test

[asset-buyer] Fix test (assetData string)

packages/asset-buyer/src/asset_buyer.ts

@@ -193,6 +193,7 @@ export class AssetBuyer {
     ): Promise<LiquidityForAssetData> {
         const shouldForceOrderRefresh =
             options.shouldForceOrderRefresh !== undefined ? options.shouldForceOrderRefresh : false;
+        assert.isString('assetData', assetData);
         assetDataUtils.decodeAssetDataOrThrow(assetData);
         assert.isBoolean('options.shouldForceOrderRefresh', shouldForceOrderRefresh);