Empty sensitive_values when viewing json representation of out file

I am planning a root module that includes an RDS, a parameter group and so forth.

The config for the parameter group is more or less:

resource "aws_db_parameter_group" "my-pg-postgres-12-3" {
  provider = aws.us_east_1
  name     = "my-pg-postgres-12-3"
  family   = "postgres12"

  parameter {
    name         = "application_name"
    value        = "psql non-interactive"
    apply_method = "immediate"
  }

  parameter {
    name         = "autovacuum"
    value        = 1
    apply_method = "immediate"
  }
.
.
.
// many more parameters following...

I am running terraform plan -out planfile and then terraform show --json planfile

I noticed the following in the json representation of my parameter group

        {
          "address": "aws_db_parameter_group.production-my-postgres-12-3",
          "mode": "managed",
          "type": "aws_db_parameter_group",
          "name": "production-my-postgres-12-3",
          "provider_name": "registry.terraform.io/hashicorp/aws",
          "schema_version": 0,
          "values": {
            "description": "Managed by Terraform",
            "family": "postgres9.6",
            "name": "production-my-postgres-9-6",
            "parameter": [
              {
                "apply_method": "immediate",
                "name": "application_name",
                "value": "psql non-interactive"
              },
              {
                "apply_method": "immediate",
                "name": "autovacuum",
                "value": "1"
              },
              {
                "apply_method": "immediate",
                "name": "lc_messages",
                "value": "en_US.UTF-8"
              },
              {
                "apply_method": "immediate",
                "name": "lc_monetary",
                "value": "en_US.UTF-8"
              },
              {
                "apply_method": "immediate",
                "name": "lc_numeric",
                "value": "en_US.UTF-8"
              },
              {
                "apply_method": "immediate",
                "name": "lc_time",
                "value": "en_US.UTF-8"
              },
              {
                "apply_method": "immediate",
                "name": "log_autovacuum_min_duration",
                "value": "30000"
              },
              {
                "apply_method": "immediate",
                "name": "log_connections",
                "value": "1"
              },
              {
                "apply_method": "immediate",
                "name": "log_lock_waits",
                "value": "true"
              },
              {
                "apply_method": "immediate",
                "name": "log_min_duration_statement",
                "value": "2000"
              },
              {
                "apply_method": "immediate",
                "name": "log_temp_files",
                "value": "10240"
              },
              {
                "apply_method": "immediate",
                "name": "maintenance_work_mem",
                "value": "2147483647"
              },
              {
                "apply_method": "immediate",
                "name": "max_parallel_workers_per_gather",
                "value": "3"
              },
              {
                "apply_method": "immediate",
                "name": "max_standby_archive_delay",
                "value": "36000000"
              },
              {
                "apply_method": "immediate",
                "name": "max_standby_streaming_delay",
                "value": "36000000"
              },
              {
                "apply_method": "immediate",
                "name": "wal_keep_segments",
                "value": "64"
              },
              {
                "apply_method": "immediate",
                "name": "work_mem",
                "value": "122000000"
              },
              {
                "apply_method": "pending-reboot",
                "name": "max_connections",
                "value": "500"
              },
              {
                "apply_method": "pending-reboot",
                "name": "max_replication_slots",
                "value": "20"
              },
              {
                "apply_method": "pending-reboot",
                "name": "max_worker_processes",
                "value": "20"
              },
              {
                "apply_method": "pending-reboot",
                "name": "rds.force_ssl",
                "value": "false"
              },
              {
                "apply_method": "pending-reboot",
                "name": "shared_preload_libraries",
                "value": "pg_stat_statements"
              }
            ],
            "tags": {
              "Provisioner": "Terraform"
            },
            "tags_all": {
              "Provisioner": "Terraform"
            }
          },
          "sensitive_values": {
            "parameter": [
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {},
              {}
            ],
            "tags": {},
            "tags_all": {}
          }
        },

Why is there an array sensitive_values with so many entries?

How does this field work?

In my rds declaration (where there is nothing sensitive either) I see the following

          "sensitive_values": {
            "replicas": [],
            "restore_to_point_in_time": [],
            "s3_import": [],
            "tags": {},
            "tags_all": {},
            "vpc_security_group_ids": []
          }

What is the rationale behind the construction of this field?

(I didn’t state as sensitive e.g. the s3_import no the replicas fields etc)