Fix JDBC type validation to check for empty strings in Postgres

[liferoad]

Fixes #35198

025-09-09T17:57:22.3193168Z =========================== short test summary info ============================
2025-09-09T17:57:22.3194694Z FAILED apache_beam/yaml/integration_tests.py::PostgresTest::test_only - ValueError: Error applying transform "WriteToPostgres" at line 33: java.lang.IllegalArgumentException: Wrong JDBC type. Expected 'postgres' but got ''
2025-09-09T17:57:22.3196717Z 	at org.apache.beam.sdk.io.jdbc.providers.WriteToPostgresSchemaTransformProvider.from(WriteToPostgresSchemaTransformProvider.java:63)
2025-09-09T17:57:22.3198431Z 	at org.apache.beam.sdk.io.jdbc.providers.WriteToPostgresSchemaTransformProvider.from(WriteToPostgresSchemaTransformProvider.java:36)
2025-09-09T17:57:22.3200284Z 	at org.apache.beam.sdk.schemas.transforms.TypedSchemaTransformProvider.from(TypedSchemaTransformProvider.java:111)
2025-09-09T17:57:22.3202104Z 	at org.apache.beam.sdk.expansion.service.ExpansionServiceSchemaTransformProvider.getTransform(ExpansionServiceSchemaTransformProvider.java:137)
2025-09-09T17:57:22.3203904Z 	at org.apache.beam.sdk.expansion.service.ExpansionService$TransformProviderForPayloadTranslator.getTransform(ExpansionService.java:263)
2025-09-09T17:57:22.3205314Z 	at org.apache.beam.sdk.expansion.service.TransformProvider.apply(TransformProvider.java:121)
2025-09-09T17:57:22.3206436Z 	at org.apache.beam.sdk.expansion.service.ExpansionService.expand(ExpansionService.java:657)
2025-09-09T17:57:22.3207518Z 	at org.apache.beam.sdk.expansion.service.ExpansionService.expand(ExpansionService.java:758)
2025-09-09T17:57:22.3208770Z 	at org.apache.beam.model.expansion.v1.ExpansionServiceGrpc$MethodHandlers.invoke(ExpansionServiceGrpc.java:306)
2025-09-09T17:57:22.3210315Z 	at org.apache.beam.vendor.grpc.v1p69p0.io.grpc.stub.ServerCalls$UnaryServerCallHandler$UnaryServerCallListener.onHalfClose(ServerCalls.java:182)
2025-09-09T17:57:22.3212054Z 	at org.apache.beam.vendor.grpc.v1p69p0.io.grpc.internal.ServerCallImpl$ServerStreamListenerImpl.halfClosed(ServerCallImpl.java:356)
2025-09-09T17:57:22.3213774Z 	at org.apache.beam.vendor.grpc.v1p69p0.io.grpc.internal.ServerImpl$JumpToApplicationThreadServerStreamListener$1HalfClosed.runInContext(ServerImpl.java:861)
2025-09-09T17:57:22.3215505Z 	at org.apache.beam.vendor.grpc.v1p69p0.io.grpc.internal.ContextRunnable.run(ContextRunnable.java:37)
2025-09-09T17:57:22.3216814Z 	at org.apache.beam.vendor.grpc.v1p69p0.io.grpc.internal.SerializingExecutor.run(SerializingExecutor.java:133)
2025-09-09T17:57:22.3218012Z 	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
2025-09-09T17:57:22.3219129Z 	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
2025-09-09T17:57:22.3219926Z 	at java.base/java.lang.Thread.run(Thread.java:829)
2025-09-09T17:57:22.3220360Z 
2025-09-09T17:57:22.3220369Z 
2025-09-09T17:57:22.3220855Z java.lang.IllegalArgumentException: Wrong JDBC type. Expected 'postgres' but got ''

https://productionresultssa0.blob.core.windows.net/actions-results/a9bd2633-9ccb-4bb2-8ccf-21615d49b6d6/workflow-job-run-0f8530dd-c0d8-5110-bc4c-cd0b75d084b9/logs/job/job-logs.txt?rsct=text%2Fplain&se=2025-09-09T18%3A54%3A01Z&sig=y0KMBQT0dBpYy99Lm4COR1H3wPjUHpuRnN9%2B0UtW7e0%3D&ske=2025-09-10T06%3A20%3A17Z&skoid=ca7593d4-ee42-46cd-af88-8b886a2f84eb&sks=b&skt=2025-09-09T18%3A20%3A17Z&sktid=398a6654-997b-47e9-b12b-9515b896b4de&skv=2025-05-05&sp=r&spr=https&sr=b&st=2025-09-09T18%3A43%3A56Z&sv=2025-05-05

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[gemini-code-assist]

Summary of Changes

Hello @liferoad, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a bug in the JDBC type validation for Postgres connectors. Previously, an empty string provided for the jdbcType parameter would bypass the null check but still cause an IllegalArgumentException. The fix ensures that empty strings are now correctly identified and rejected, improving the robustness of the data pipeline's interaction with Postgres databases.

Highlights

• JDBC Type Validation Fix: Enhanced the JDBC type validation logic for both reading from and writing to Postgres. The change specifically adds a check to ensure that the jdbcType parameter is not an empty string, preventing IllegalArgumentException when an empty string is provided instead of null or a valid type.

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[shunping]

LGTM! Thanks for fixing this.

[github-actions]

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R: @m-trieu for label java.

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[Amar3tto]

Let's cherrypick this to release-2.68

[liferoad]

Let's cherrypick this to release-2.68

I do not think we need this for 2.68 since #36034 was merged after the cut.