Cryptic error returned when trying to add a POLine to an Open PO

## Create PO ##
curl 'http://folio-testing-backend01.aws.indexdata.com:9130/orders/composite-orders' -H "X-Okapi-Token: $TOKEN" -H 'Content-Type: application/json' -w '\n' --data-binary '{
>    "id" : "15d97111-ed48-4369-b8eb-269363aabf43",
>    "po_number" : "MODORDERS188",
>    "order_type" : "One-Time",
>    "vendor" : "4837d297-443c-48f2-b3b2-4eda69da8ef3",
>    "workflow_status" : "Pending",
>    "compositePoLines" : [ ],
>    "metadata" : {
>      "createdDate" : "2019-03-07T21:30:09.547+0000",
>      "createdByUserId" : "49e74bca-d8c2-5399-be7c-379fffa1aa6f",
>      "updatedDate" : "2019-03-07T21:30:09.547+0000",
>      "updatedByUserId" : "49e74bca-d8c2-5399-be7c-379fffa1aa6f"
>    }
>  }'
{
  "id" : "15d97111-ed48-4369-b8eb-269363aabf43",
  "notes" : [ ],
  "po_number" : "MODORDERS188",
  "order_type" : "One-Time",
  "vendor" : "4837d297-443c-48f2-b3b2-4eda69da8ef3",
  "workflow_status" : "Pending",
  "compositePoLines" : [ ],
  "metadata" : {
    "createdDate" : "2019-03-07T21:36:12.419+0000",
    "createdByUserId" : "49e74bca-d8c2-5399-be7c-379fffa1aa6f",
    "updatedDate" : "2019-03-07T21:36:12.419+0000",
    "updatedByUserId" : "49e74bca-d8c2-5399-be7c-379fffa1aa6f"
  }
}

## Transition to Open ##
curl 'http://folio-testing-backend01.aws.indexdata.com:9130/orders/composite-orders/15d97111-ed48-4369-b8eb-269363aabf43' -H "X-Okapi-Token: $TOKEN" -H 'Content-Type: application/json' -w '\n' -XPUT --data-binary '
> {
>   "id" : "15d97111-ed48-4369-b8eb-269363aabf43",
>   "notes" : [ ],
>   "po_number" : "MODORDERS188",
>   "order_type" : "One-Time",
>   "vendor" : "4837d297-443c-48f2-b3b2-4eda69da8ef3",
>   "workflow_status" : "Open",
>   "compositePoLines" : [ ]
> }'

## Sanity Check ##
curl 'http://folio-testing-backend01.aws.indexdata.com:9130/orders/composite-orders/15d97111-ed48-4369-b8eb-269363aabf43' -H "X-Okapi-Token: $TOKEN" -H 'Content-Type: application/json' -w '\n' -XGET
{
  "id" : "15d97111-ed48-4369-b8eb-269363aabf43",
  "dateOrdered" : "2019-03-07T21:37:40.208+0000",
  "notes" : [ ],
  "po_number" : "MODORDERS188",
  "order_type" : "One-Time",
  "vendor" : "4837d297-443c-48f2-b3b2-4eda69da8ef3",
  "workflow_status" : "Open",
  "compositePoLines" : [ ],
  "metadata" : {
    "createdDate" : "2019-03-07T21:36:12.441+0000",
    "createdByUserId" : "49e74bca-d8c2-5399-be7c-379fffa1aa6f",
    "updatedDate" : "2019-03-07T21:37:40.221+0000",
    "updatedByUserId" : "49e74bca-d8c2-5399-be7c-379fffa1aa6f"
  }
}

## Add a POLine ##
curl 'http://folio-testing-backend01.aws.indexdata.com:9130/orders/order-lines' -H "X-Okapi-Token: $TOKEN" -H 'Content-Type: application/json' -w'\n' --data-binary '{  
>    "source":{  
>       "code":"FOLIO"
>    },
>    "cost":{  
>       "currency":"USD",
>       "list_price":"5.99",
>       "quantity_physical":1
>    },
>    "vendor_detail":{  
>       "instructions":""
>    },
>    "purchase_order_id":"15d97111-ed48-4369-b8eb-269363aabf43",
>    "acquisition_method":"Gift",
>    "order_format":"Physical Resource",
>    "title":"Grass",
>    "contributors":[  
>       {  
>          "contributor":"Sheri S. Tepper"
>       }
>    ],
>    "details":{  
>       "product_ids":[  
>          {  
>             "product_id":"9788675309",
>             "product_id_type":"ISBN"
>          }
>       ],
>       "material_types":[  
>          "1a54b431-2e4f-452d-9cae-9cee66c9a892"
>       ]
>    },
>    "locations":[  
>       {  
>          "location_id":"53cf956f-c1df-410b-8bea-27f712cca7c0",
>          "quantity_physical":1
>       }
>    ]
> }' 
{
  "errors" : [ {
    "message" : "ErrorMessage(fields=Map(Position -> 23, Line -> 420, File -> namespace.c, SQLSTATE -> 42P01, Routine -> RangeVarGetRelidExtended, V -> ERROR, Message -> relation \"polNumber_15d97111-ed48-4369-b8eb-269363aabf43\" does not exist, Severity -> ERROR))",
    "code" : "genericError",
    "parameters" : [ ]
  } ]
}