Fix null return value of GEODIST command.

Relates to: #1797

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

@@ -53,6 +53,7 @@ import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.Future;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.function.Function;
 import java.util.function.Supplier;
 
 import org.springframework.beans.BeanUtils;
@@ -936,6 +937,79 @@ public class LettuceConnection extends AbstractRedisConnection {
 		}
 	}
 
+	<S, T> void executeInPipeline(Function<RedisClusterAsyncCommands, RedisFuture<S>> command,
+			Converter<S, T> converter) {
+
+		try {
+			pipeline(newLettuceResult(command.apply(getAsyncConnection()), converter));
+		} catch (Exception ex) {
+			throw convertLettuceAccessException(ex);
+		}
+	}
+
+	<S, T> void executeInTx(Function<RedisClusterAsyncCommands, RedisFuture<S>> command, Converter<S, T> converter) {
+
+		try {
+			transaction(newLettuceResult(command.apply(getAsyncConnection()), converter));
+		} catch (Exception ex) {
+			throw convertLettuceAccessException(ex);
+		}
+	}
+
+	<T> NullableResult<T> execute(Function<RedisClusterCommands, T> command) {
+
+		try {
+
+			T result = command.apply(getConnection());
+			return NullableResult.of(result);
+		} catch (Exception ex) {
+			throw convertLettuceAccessException(ex);
+		}
+	}
+
+	<T> RedisFuture<T> executeAsync(Function<RedisClusterAsyncCommands, RedisFuture<T>> command) {
+
+		try {
+			return command.apply(getAsyncConnection());
+		} catch (Exception ex) {
+			throw convertLettuceAccessException(ex);
+		}
+	}
+
+	<S, T> T invoke(RedisFuture<S> future, Converter<S, T> converter) {
+
+		if (isPipelined()) {
+			pipeline(newLettuceResult(future, converter));
+			return null;
+		}
+		if (isQueueing()) {
+			transaction(newLettuceResult(future, converter));
+			return null;
+		}
+		return NullableResult.of((S) await(future)).convert(converter).get();
+	}
+
+	<T> T execute(Function<RedisClusterCommands, T> sync, Function<RedisClusterAsyncCommands, RedisFuture<T>> async) {
+		return execute(sync, async, val -> val);
+	}
+
+	// use a future here and only async.
+	<S, T> T execute(Function<RedisClusterCommands, S> sync, Function<RedisClusterAsyncCommands, RedisFuture<S>> async,
+			Converter<S, T> converter) {
+
+		if (isPipelined()) {
+			executeInPipeline(async, converter);
+			return null;
+		}
+		if (isQueueing()) {
+			executeInTx(async, converter);
+			return null;
+		}
+
+		// return execute(sync).convert(converter).get();
+		return NullableResult.of((S) await(executeAsync(async))).convert(converter).get();
+	}
+
 	void transaction(FutureResult<?> result) {
 		txResults.add(result);
 	}

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

@@ -36,6 +36,7 @@ import org.springframework.data.geo.Distance;
 import org.springframework.data.geo.GeoResults;
 import org.springframework.data.geo.Metric;
 import org.springframework.data.geo.Point;
+import org.springframework.data.redis.connection.NullableResult;
 import org.springframework.data.redis.connection.RedisGeoCommands;
 import org.springframework.data.redis.connection.convert.ListConverter;
 import org.springframework.lang.Nullable;
@@ -165,23 +166,12 @@ class LettuceGeoCommands implements RedisGeoCommands {
 		GeoArgs.Unit geoUnit = LettuceConverters.toGeoArgsUnit(metric);
 		Converter<Double, Distance> distanceConverter = LettuceConverters.distanceConverterForMetric(metric);
 
-		try {
-			if (isPipelined()) {
-				pipeline(connection.newLettuceResult(getAsyncConnection().geodist(key, member1, member2, geoUnit),
-						distanceConverter));
-				return null;
-			}
-			if (isQueueing()) {
-				transaction(connection.newLettuceResult(getAsyncConnection().geodist(key, member1, member2, geoUnit),
-						distanceConverter));
-				return null;
-			}
+//		return connection.execute(
+//				sync -> sync.geodist(key, member1, member2, geoUnit),
+//				async -> async.geodist(key, member1, member2, geoUnit),
+//				distanceConverter);
 
-			Double distance = getConnection().geodist(key, member1, member2, geoUnit);
-			return distance != null ? distanceConverter.convert(distance) : null;
-		} catch (Exception ex) {
-			throw convertLettuceAccessException(ex);
-		}
+		return connection.invoke(connection.getAsyncConnection().geodist(key, member1, member2, geoUnit), distanceConverter);
 	}
 
 	/*