fix: address comments

Author: jinseopkim0

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/admin/v2/BigtableTableAdminClient.java

@@ -1460,25 +1460,6 @@ public ApiFuture<Void> awaitReplicationAsync(final String tableId) {
     return stub.awaitReplicationCallable().futureCall(tableName);
   }
 
-  /**
-   * Generates a consistency token and polls it until replication is consistent. Blocks until
-   * completion.
-   *
-   * @param tableId The table to check.
-   */
-  public void waitForConsistency(String tableId) {
-    awaitReplication(tableId);
-  }
-
-  /**
-   * Asynchronously generates a token and polls until consistent.
-   *
-   * @param tableId The table to check.
-   */
-  public ApiFuture<Void> waitForConsistencyAsync(String tableId) {
-    return awaitReplicationAsync(tableId);
-  }
-
   /**
    * Polls an existing consistency token until replication is consistent. Useful for checking
    * consistency of a token generated in a separate process. Blocks until completion.

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/admin/v2/models/ConsistencyRequest.java

@@ -23,6 +23,7 @@
 import com.google.bigtable.admin.v2.StandardReadRemoteWrites;
 import com.google.bigtable.admin.v2.TableName;
 import com.google.cloud.bigtable.data.v2.internal.TableAdminRequestContext;
+import com.google.common.base.Preconditions;
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
@@ -51,9 +52,12 @@ public static ConsistencyRequest forReplication(String tableId) {
    * Creates a request to check consistency using an existing token.
    *
    * @param tableId The table ID.
-   * @param consistencyToken The token to check.
+   * @param consistencyToken The token to check. Must not be null.
+   * @throws NullPointerException if consistencyToken is null.
    */
   public static ConsistencyRequest forReplication(String tableId, String consistencyToken) {
+    Preconditions.checkNotNull(consistencyToken, "consistencyToken must not be null");
+
     return new AutoValue_ConsistencyRequest(
         tableId, CheckConsistencyRequest.ModeCase.STANDARD_READ_REMOTE_WRITES, consistencyToken);
   }