Preparation for Avro update (#2650)

hudi-common/src/main/avro/HoodieClusteringPlan.avsc

@@ -30,7 +30,7 @@
     },
     {
        "name":"strategy",
-       "type":["HoodieClusteringStrategy", "null"],
+       "type":["null", "HoodieClusteringStrategy"],
        "default": null
     },
     {

hudi-common/src/main/avro/HoodieFSPermission.avsc

@@ -28,22 +28,22 @@
       {
         "name":"userAction",
         "type":[ "null", "string" ],
-        "default": "null"
+        "default": null
       },
       {
         "name":"groupAction",
         "type":[ "null", "string" ],
-        "default": "null"
+        "default": null
       },
       {
         "name":"otherAction",
         "type":[ "null", "string" ],
-        "default": "null"
+        "default": null
       },
       {
         "name":"stickyBit",
         "type":[ "null", "boolean" ],
-        "default": "null"
+        "default": null
       }
    ]
 }

hudi-common/src/main/avro/HoodieRequestedReplaceMetadata.avsc

@@ -23,11 +23,11 @@
      {
          "name":"operationType",
          "type":["null", "string"],
-         "default": ""
+         "default": null
     },
     {
        "name":"clusteringPlan", /* only set if operationType == clustering" */
-       "type":["HoodieClusteringPlan", "null"],
+       "type":["null", "HoodieClusteringPlan"],
        "default": null
     },
     {

hudi-common/src/main/avro/HoodieRestoreMetadata.avsc

@@ -38,7 +38,7 @@
      /* overlaps with 'instantsToRollback' field. Adding this to track action type for all the instants being rolled back. */
      {
        "name": "restoreInstantInfo",
-       "default": null,
+       "default": [],
        "type": {
          "type": "array",
          "default": null,