filter out empty string for default parameters

Author: jeffhwang-sq

service/src/main/kotlin/app/cash/backfila/ui/actions/BackfillCreateHandlerAction.kt

@@ -55,7 +55,7 @@ class BackfillCreateHandlerAction @Inject constructor(
       formFields[BackfillCreateField.THREADS_PER_PARTITION.fieldId]?.ifNotBlank { createRequestBuilder.num_threads(it.toIntOrNull()) }
       formFields[BackfillCreateField.EXTRA_SLEEP_MS.fieldId]?.ifNotBlank { createRequestBuilder.extra_sleep_ms(it.toLongOrNull()) }
       formFields[BackfillCreateField.BACKOFF_SCHEDULE.fieldId]?.ifNotBlank { createRequestBuilder.backoff_schedule(it) }
-      val customParameters = formFields.filter { it.key.startsWith(BackfillCreateField.CUSTOM_PARAMETER_PREFIX.fieldId) }
+      val customParameters = formFields.filter { it.key.startsWith(BackfillCreateField.CUSTOM_PARAMETER_PREFIX.fieldId) && !it.value.isNullOrBlank() }
         .map { it.key.removePrefix(BackfillCreateField.CUSTOM_PARAMETER_PREFIX.fieldId) to it.value?.encodeUtf8() }.toMap()
       if (customParameters.isNotEmpty()) {
         createRequestBuilder.parameter_map(customParameters)