Description of problem:
-----------------------

A GET of Crush rule lists some values as null for the "steps".
        "steps": [
            {
                "op": "take", 
                "type": null, 
                "num": null, 
                "item_name": "default", 
                "item": -1
            }, 
            {
                "op": "chooseleaf_firstn", 
                "type": "host", 
                "num": 0, 
                "item_name": null, 
                "item": null
            }, 
            {
                "op": "emit", 
                "type": null, 
                "num": null, 
                "item_name": null, 
                "item": null
            }

But the CLI the command " ceph osd crush rule dump" does not list that way. It lists as follows:

    "steps": [
        {
            "op": "take",
            "item": -1,
            "item_name": "default"
        },
        {
            "op": "chooseleaf_firstn",
            "num": 0,
            "type": "host"
        },
        {
            "op": "emit"
        }

Version-Release number of selected component (if applicable):
ceph version 10.2.1-7.el7cp (339d1fb5d73e5f113c8538a45e95b3777038da36)
calamari-server-1.4.0-0.10.rc13.el7cp.x86_64


How reproducible: always


Steps to Reproduce:
1. invoke https://<mon-ip>:8002/api/v2/cluster/<fs id>/crush_rule

Actual results:
Displays null for few values under "steps" section.

Expected results:
Should not display null values

Additional info:
The PATCH operation fails if we use null values