allow setting table.file.ec.policy to '' (#5945)

Author: keith-turner

server/base/src/main/java/org/apache/accumulo/server/util/PropUtil.java

@@ -78,7 +78,8 @@ protected static void validateProperties(final ServerContext context,
         }
       }
 
-      if (prop.getKey().equals(Property.TABLE_ERASURE_CODE_POLICY.getKey())) {
+      if (prop.getKey().equals(Property.TABLE_ERASURE_CODE_POLICY.getKey())
+          && !prop.getValue().isEmpty()) {
         var volumes = context.getVolumeManager().getVolumes();
         for (var volume : volumes) {
           if (volume.getFileSystem() instanceof DistributedFileSystem) {

test/src/main/java/org/apache/accumulo/test/compaction/ErasureCodeIT.java

@@ -277,6 +277,11 @@ public void test() throws Exception {
       c.tableOperations().setProperty(table1, Property.TABLE_ERASURE_CODE_POLICY.getKey(), policy2);
       assertEquals(policy2, c.tableOperations().getConfiguration(table1)
           .get(Property.TABLE_ERASURE_CODE_POLICY.getKey()));
+      // should be able to set it to the default value
+      c.tableOperations().setProperty(table1, Property.TABLE_ERASURE_CODE_POLICY.getKey(),
+          Property.TABLE_ERASURE_CODE_POLICY.getDefaultValue());
+      assertEquals(Property.TABLE_ERASURE_CODE_POLICY.getDefaultValue(), c.tableOperations()
+          .getConfiguration(table1).get(Property.TABLE_ERASURE_CODE_POLICY.getKey()));
     }
   }
 }