Verify if IAM policy validation is needed when received from API

[frankyn]

IllegalStateException in PolicyHelper.java:

We should replace with a warning potentially; the part that isn't clear is that it's converting IAM policy from Apiary to Manual representation which we need to be careful about.

Cases check:

• Is it possible to have an empty storage bucket bindings list while having inherited permissions from project level? Yes.

Prerequesites

1. Grant roles/storage.admin to your user account and service account principals.
2. Create a standard class type bucket in any region (will occur for both UBLA and Fine Grained buckets)
3. Remove default Viewer, Editor, and Owner principal assignments on the new bucket

Reproductions

Using https://developers.google.com/oauthplayground/:

Request / Response
GET /storage/v1/b/iam-issue-1175/iam HTTP/1.1
Host: storage.googleapis.com
Content-length: 0
Authorization: X
HTTP/1.1 200 OK
Content-length: 118
Content-location: https://storage.googleapis.com/storage/v1/b/iam-issue-1175/iam
Expires: Mon, 13 Dec 2021 19:28:04 GMT
Vary: Origin,X-Origin
Cache-control: private, max-age=0, must-revalidate, no-transform
Etag: CAQ=
X-guploader-uploadid: ADPycdtqlzOMYDU_dsPGQi7e0DthKx5_AL40IL6aHnDf8Fi3YBRihhNpOc6-RHCulknFYxowRkir_Khdkg5mNqP5NLSTbQK-QQ
Date: Mon, 13 Dec 2021 19:28:04 GMT
Content-type: application/json; charset=UTF-8
{
  "resourceId": "projects/_/buckets/iam-issue-1175", 
  "kind": "storage#policy", 
  "version": 1, 
  "etag": "CAQ="
}

Using Java Storage client

@Test
  public void testGetIamPolicy() {
    Storage client = StorageOptions.getDefaultInstance().getService();
    client.getIamPolicy("iam-issue-1175");
  }

/*
java.lang.IllegalStateException: Missing required bindings.

	at com.google.cloud.storage.PolicyHelper.convertFromApiPolicy(PolicyHelper.java:54)
	at com.google.cloud.storage.Retrying.run(Retrying.java:52)
	at com.google.cloud.storage.StorageImpl.run(StorageImpl.java:1374)
	at com.google.cloud.storage.StorageImpl.getIamPolicy(StorageImpl.java:1316)
	at com.google.cloud.storage.it.ITIamPolicy.testGetIamPolicy(ITIamPolicy.java:12)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
	at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
	at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
*/

related bug: #1159