Fix LPOS when member not in list.

This commit ensures an empty List is returned in the case the member does not exist in the target list.

See #1957.
Original pull request: #1962.

src/main/java/org/springframework/data/redis/connection/jedis/JedisListCommands.java

@@ -72,7 +72,7 @@ class JedisListCommands implements RedisListCommands {
 			return connection.invoke().just(BinaryJedis::lpos, MultiKeyPipelineBase::lpos, key, element, params, count);
 		}
 
-		return connection.invoke().from(BinaryJedis::lpos, MultiKeyPipelineBase::lpos, key, element, params).get(Collections::singletonList);
+		return connection.invoke().from(BinaryJedis::lpos, MultiKeyPipelineBase::lpos, key, element, params).getOrElse(Collections::singletonList, Collections::emptyList);
 	}
 
 	/*

src/main/java/org/springframework/data/redis/connection/lettuce/LettuceListCommands.java

@@ -71,7 +71,7 @@ class LettuceListCommands implements RedisListCommands {
 			return connection.invoke().just(RedisListAsyncCommands::lpos, key, element, count, args);
 		}
 
-		return connection.invoke().from(RedisListAsyncCommands::lpos, key, element, args).get(Collections::singletonList);
+		return connection.invoke().from(RedisListAsyncCommands::lpos, key, element, args).getOrElse(Collections::singletonList, Collections::emptyList);
 	}
 
 	/*

src/test/java/org/springframework/data/redis/connection/AbstractConnectionIntegrationTests.java

@@ -1464,6 +1464,16 @@ public abstract class AbstractConnectionIntegrationTests {
 		assertThat((List<Long>) getResults().get(1)).containsExactly(2L, 6L, 7L);
 	}
 
+	@Test // GH-1957
+	@EnabledOnCommand("LPOS")
+	void lPosNonExisting() {
+
+		actual.add(connection.rPush("mylist", "a", "b", "c", "1", "2", "3", "c", "c"));
+		actual.add(connection.lPos("mylist", "x", null, null));
+
+		assertThat((List<Long>) getResults().get(1)).isEmpty();
+	}
+
 	// Set operations
 
 	@Test

src/test/java/org/springframework/data/redis/connection/jedis/JedisClusterConnectionTests.java

@@ -2534,4 +2534,14 @@ public class JedisClusterConnectionTests implements ClusterConnectionTests {
 
 		assertThat(result).containsExactly(2L, 6L, 7L);
 	}
+
+	@Test // GH-1957
+	@EnabledOnCommand("LPOS")
+	void lPosNonExisting() {
+
+		nativeConnection.rpush(KEY_1, "a", "b", "c", "1", "2", "3", "c", "c");
+		List<Long> result = clusterConnection.listCommands().lPos(KEY_1_BYTES, "x".getBytes(StandardCharsets.UTF_8), null, null);
+
+		assertThat(result).isEmpty();
+	}
 }