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Spanner Null Array Values Issue

This project reproduces an issue with Spring Cloud GCP Spanner where null elements inside arrays cause a NullPointerException during deserialization when reading entities from the database.

The Issue

When saving an entity with a List<Long> field (mapped to Spanner's ARRAY<INT64> column type) that contains null elements (e.g., [1L, null]), the following behavior occurs:

  • ✅ Save operation succeeds - The entity is successfully written to Spanner
  • ✅ existsById() succeeds - The entity can be verified as existing
  • ❌ findById() fails - Reading the entity back throws NullPointerException

Schema

CREATE TABLE example_entity (
  id INT64 NOT NULL,
  values ARRAY<INT64>
) PRIMARY KEY (id)

Error Details

java.lang.NullPointerException: Cannot invoke "Object.getClass()" because "sourceValue" is null

The error occurs in Spring Data Spanner's conversion layer when attempting to deserialize the array from Spanner. The converter doesn't properly handle null elements within arrays, even though:

  • Spanner itself supports null values in arrays
  • The data is successfully stored in the database

Running the Reproduction

Prerequisites

  • Java 17
  • Docker and Docker Compose
  • Maven (or use included mvnw)

Steps

  1. Start the Spanner Emulator

    docker-compose up -d

    This starts:

    • Spanner emulator on ports 9010 (gRPC) and 9020 (HTTP)
    • Instance initialization to create the emulator instance and database

  2. Run the Test

    ./mvnw test

    The test will:

    • Create the example_entity table
    • Save an ExampleEntity with values = [1L, null]
    • Verify the entity exists
    • Attempt to retrieve the entity (this will fail with NullPointerException)

Expected Output

[ERROR] Errors:
[ERROR]   ExampleTest.testSaveAndFindById:49 » NullPointer Cannot invoke "Object.getClass()" because "sourceValue" is null

Project Structure

  • ExampleEntity.java - Entity with a List<Long> field that can contain nulls
  • ExampleRepository.java - Spring Data repository extending SpannerRepository
  • ExampleTest.java - Test that reproduces the issue
  • application.properties - Configuration to connect to the Spanner emulator

Configuration

The application is configured to use the local Spanner emulator:

spring.cloud.gcp.spanner.emulator.enabled=true
spring.cloud.gcp.spanner.emulator-host=localhost:9010
spring.cloud.gcp.spanner.project-id=emulator
spring.cloud.gcp.spanner.instance-id=emulator
spring.cloud.gcp.spanner.database=emulator

Cleanup

docker-compose down