fix nil entry crash

[shuyama1]

Fixes hashicorp/terraform-provider-google#11212

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Ran relevant acceptance tests (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

dataproc: fixed a crash when `logging_config` only contains `nil` entry  in `google_dataproc_workflow_template`

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 13 files changed, 30 insertions(+), 30 deletions(-))
Terraform Beta: Diff ( 13 files changed, 30 insertions(+), 30 deletions(-))
TF Validator: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 16 files changed, 174 insertions(+), 174 deletions(-))
Terraform Beta: Diff ( 18 files changed, 185 insertions(+), 185 deletions(-))
TF Validator: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccDatasourceGoogleServiceNetworkingPeeredDnsDomain_basic|TestAccDataSourceSqlDatabaseInstance_basic|TestAccApikeysKey_AndroidKey|TestAccApikeysKey_BasicKey|TestAccApikeysKey_IosKey|TestAccApikeysKey_ServerKey|TestAccApikeysKey_MinimalKey|TestAccArtifactRegistryRepository_create_mvn_snapshot|TestAccArtifactRegistryRepository_create_mvn_release|TestAccBigqueryReservationAssignment_BasicHandWritten|TestAccCGCSnippet_sqlMysqlInstanceBackupExample|TestAccCGCSnippet_sqlPostgresInstanceBackupExample|TestAccCGCSnippet_sqlSqlserverInstanceBackupExample|TestAccCGCSnippet_sqlMysqlInstanceAuthorizedNetworkExample|TestAccCGCSnippet_sqlSqlserverInstanceBackupLocationExample|TestAccCloudBuildTrigger_cloudbuildTriggerFilenameExample|TestAccCloudBuildTrigger_cloudbuildTriggerPubsubConfigExample|TestAccCloudBuildTrigger_cloudbuildTriggerWebhookConfigExample|TestAccCloudBuildTrigger_cloudbuildTriggerManualExample|TestAccCloudBuildTrigger_cloudbuildTriggerBuildExample|TestAccCloudBuildTrigger_basic|TestAccCloudBuildTrigger_available_secrets_config|TestAccCloudBuildTrigger_cloudbuildTriggerServiceAccountExample|TestAccCloudBuildTrigger_disable|TestAccCloudBuildTrigger_fullStep|TestAccCloudFunctionsFunction_secretEnvVar|TestAccContainerAwsCluster_BasicHandWritten|TestAccContainerCluster_withAuthenticatorGroupsConfig|TestAccContainerNodePool_gvnic|TestAccDataprocCluster_nonPreemptibleSecondary|TestAccDataprocCluster_updatable|TestAccDataprocCluster_withConfigOverrides|TestAccNetworkServicesEdgeCacheService_networkServicesEdgeCacheServiceAdvancedExample You can view the result here: https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=268116

[modular-magician]

Tests failed during RECORDING mode: TestAccContainerCluster_withAuthenticatorGroupsConfig|TestAccDataSourceSqlDatabaseInstance_basic|TestAccNetworkServicesEdgeCacheService_networkServicesEdgeCacheServiceAdvancedExample Please fix these to complete your PR