Qdrant vector source unsupport null value in metadata

[lanyuanxiaoyao]

Bug description
NullPointerException when null value in metadata.
toObjectMapuse Collectors.toMap to create map, but it unsupport null value. Qdrant allow null value in metadata.
it may help this

spring-ai/vector-stores/spring-ai-qdrant-store/src/main/java/org/springframework/ai/vectorstore/qdrant/QdrantVectorStore.java

Line 280 in 094eeab

var metadata = QdrantObjectFactory.toObjectMap(point.getPayloadMap());

spring-ai/vector-stores/spring-ai-qdrant-store/src/main/java/org/springframework/ai/vectorstore/qdrant/QdrantObjectFactory.java

Line 44 in 094eeab

return payload.entrySet().stream().collect(Collectors.toMap(e -> e.getKey(), e -> object(e.getValue())));

Environment
Spring AI 1.0.0

[WOONBE]

I'd like to contribute to this!

[ilayaperumalg]

Addressed via #3483