MINOR: Small refactorings on KTable joins (#5540)

Reviewers: Guozhang Wang <wangguoz@gmail.com>

streams/src/main/java/org/apache/kafka/streams/kstream/internals/KTableImpl.java

@@ -359,8 +359,6 @@ public class KTableImpl<K, S, V> extends AbstractStream<K> implements KTable<K,
     public <VO, VR> KTable<K, VR> join(final KTable<K, VO> other,
                                        final ValueJoiner<? super V, ? super VO, ? extends VR> joiner,
                                        final Materialized<K, VR, KeyValueStore<Bytes, byte[]>> materialized) {
-        Objects.requireNonNull(other, "other can't be null");
-        Objects.requireNonNull(joiner, "joiner can't be null");
         Objects.requireNonNull(materialized, "materialized can't be null");
         final MaterializedInternal<K, VR, KeyValueStore<Bytes, byte[]>> materializedInternal = new MaterializedInternal<>(materialized);
         materializedInternal.generateStoreNameIfNeeded(builder, MERGE_NAME);
@@ -378,6 +376,7 @@ public class KTableImpl<K, S, V> extends AbstractStream<K> implements KTable<K,
     public <VO, VR> KTable<K, VR> outerJoin(final KTable<K, VO> other,
                                             final ValueJoiner<? super V, ? super VO, ? extends VR> joiner,
                                             final Materialized<K, VR, KeyValueStore<Bytes, byte[]>> materialized) {
+        Objects.requireNonNull(materialized, "materialized can't be null");
         final MaterializedInternal<K, VR, KeyValueStore<Bytes, byte[]>> materializedInternal = new MaterializedInternal<>(materialized);
         materializedInternal.generateStoreNameIfNeeded(builder, MERGE_NAME);
 
@@ -394,8 +393,10 @@ public class KTableImpl<K, S, V> extends AbstractStream<K> implements KTable<K,
     public <VO, VR> KTable<K, VR> leftJoin(final KTable<K, VO> other,
                                            final ValueJoiner<? super V, ? super VO, ? extends VR> joiner,
                                            final Materialized<K, VR, KeyValueStore<Bytes, byte[]>> materialized) {
+        Objects.requireNonNull(materialized, "materialized can't be null");
         final MaterializedInternal<K, VR, KeyValueStore<Bytes, byte[]>> materializedInternal = new MaterializedInternal<>(materialized);
         materializedInternal.generateStoreNameIfNeeded(builder, MERGE_NAME);
+
         return doJoin(other, joiner, materializedInternal, true, false);
     }
 
@@ -410,7 +411,6 @@ public class KTableImpl<K, S, V> extends AbstractStream<K> implements KTable<K,
         final String internalQueryableName = materializedInternal == null ? null : materializedInternal.storeName();
         final String joinMergeName = builder.newProcessorName(MERGE_NAME);
 
-
         return buildJoin(
             (AbstractStream<K>) other,
             joiner,