Do not return empty entries from state_queryStorage (#2906)

* do not return empty entries from state_queryStorage

* revert back None -> null change

* Revert "revert back None -> null change"

This reverts commit 318eb043e03b7aabbc3f176e02c15fd4595d16db.

substrate/core/test-runtime/src/lib.rs

@@ -106,6 +106,7 @@ pub enum Extrinsic {
 	AuthoritiesChange(Vec<AuthorityId>),
 	Transfer(Transfer, AccountSignature),
 	IncludeData(Vec<u8>),
+	StorageChange(Vec<u8>, Option<Vec<u8>>),
 }
 
 #[cfg(feature = "std")]
@@ -129,6 +130,7 @@ impl BlindCheckable for Extrinsic {
 				}
 			},
 			Extrinsic::IncludeData(_) => Err(runtime_primitives::BAD_SIGNATURE),
+			Extrinsic::StorageChange(key, value) => Ok(Extrinsic::StorageChange(key, value)),
 		}
 	}
 }