# RXS_ComposeJsonNull()

This subprocedure is used to add a JSON **null** element to a parent JSON Object or Array.

## Subprocedure Prototype

### IBM i 6.1+

| Field | Description |
|---|---|
| `     D RXS_ComposeJsonNull...      D                 PR                  Extproc('RXS_ComposeJsonNull')      D                                     Opdesc` |  |
| `     D  pName                              Const Like(RXS_Var64Kv_t)      D                                     Options(*Omit:*Varsize)` | Name to assign to JSON null data element. If being added to an array, the value of this parameter should be *OMIT. |
| `     D  pStructureDS                       Const LikeDS(RXS_JsonStructureDS_t)` | RXS_JsonStructureDS_t data structure containing a parent JSON Object or Json Array. |


## Example Code

### IBM i 7.1+

#### Example 1: Create JSON object with null element
```rpgle
      *--------------------------------------------------------------
      * This example creates a simple JSON object, adds a null data 
      * field to it, retrieves the created JSON, and then calls 
      * RXS_DestroyJson() to clean up.
      *--------------------------------------------------------------
     H DFTACTGRP(*NO) BNDDIR('RXSBND') ACTGRP(*CALLER)

      /copy QRPGLECPY,RXSCB

     D JSON            S                   Like(RXS_Var64Kv_t)

     D CreateJsonDS    DS                  LikeDS(RXS_CreateJsonDS_t)
     D RootDS          DS                  LikeDS(RXS_JsonStructureDS_t)
      /free
        RXS_ResetDS( CreateJsonDS : RXS_DS_TYPE_CREATEJSON );
        RXS_ResetDS( RootDS : RXS_DS_TYPE_JSONSTRUCTURE );
        
        CreateJsonDS.JsonStructureType = RXS_JSON_STRUCTURE_OBJECT;
        RootDS = RXS_CreateJson( CreateJsonDS );

        RXS_ComposeJsonNull( 'value' : RootDS );

        JSON = RXS_GetJsonString( CreateJsonDS );
        // JSON looks like:
        //
        // { "value": null }

        RXS_DestroyJson( CreateJsonDS );

        *INLR = *ON;
      /end-free
```

#### Example 2: Create JSON array with multiple null elements
```rpgle
      *--------------------------------------------------------------
      * This example creates a simple JSON array, adds 5 null data 
      * fields to it, retrieves the created JSON, and then calls 
      * RXS_DestroyJson() to clean up.
      *--------------------------------------------------------------
     H DFTACTGRP(*NO) BNDDIR('RXSBND') ACTGRP(*CALLER)

      /copy QRPGLECPY,RXSCB

     D JSON            S                   Like(RXS_Var64Kv_t)

     D CreateJsonDS    DS                  LikeDS(RXS_CreateJsonDS_t)
     D RootDS          DS                  LikeDS(RXS_JsonStructureDS_t)
     D i               S              3U 0
      /free
        RXS_ResetDS( CreateJsonDS : RXS_DS_TYPE_CREATEJSON );
        RXS_ResetDS( RootDS : RXS_DS_TYPE_JSONSTRUCTURE );
        
        CreateJsonDS.JsonStructureType = RXS_JSON_STRUCTURE_ARRAY;
        RootDS = RXS_CreateJson( CreateJsonDS );

        for i = 1 to 5;
          RXS_ComposeJsonNull( *OMIT : RootDS );
        endfor;

        JSON = RXS_GetJsonString( CreateJsonDS );
        // JSON looks like:
        //
        // [null,null,null,null,null]

        RXS_DestroyJson( CreateJsonDS );

        *INLR = *ON;
      /end-free
```

### IBM i 6.1

#### Example 1: Create JSON object with null element
```rpgle
      *--------------------------------------------------------------
      * This example creates a simple JSON object, adds a null data 
      * field to it, retrieves the created JSON, and then calls 
      * RXS_DestroyJson() to clean up.
      *--------------------------------------------------------------
     H DFTACTGRP(*NO) BNDDIR('RXSBND') ACTGRP(*CALLER)

      /define RXSV6R1
      /copy QRPGLECPY,RXSCB

     D JSON            S                   Like(RXS_Var64Kv_t)

     D CreateJsonDS    DS                  LikeDS(RXS_CreateJsonDS_t)
     D RootDS          DS                  LikeDS(RXS_JsonStructureDS_t)
      /free
        RXS_ResetDS( CreateJsonDS : RXS_DS_TYPE_CREATEJSON );
        RXS_ResetDS( RootDS : RXS_DS_TYPE_JSONSTRUCTURE );
        
        CreateJsonDS.JsonStructureType = RXS_JSON_STRUCTURE_OBJECT;
        RootDS = RXS_CreateJson( CreateJsonDS );

        RXS_ComposeJsonNull( 'value' : RootDS );

        JSON = RXS_GetJsonString( CreateJsonDS );
        // JSON looks like:
        //
        // { "value": null }

        RXS_DestroyJson( CreateJsonDS );

        *INLR = *ON;
      /end-free
```

#### Example 2: Create JSON array with multiple null elements
```rpgle
      *--------------------------------------------------------------
      * This example creates a simple JSON array, adds 5 null data 
      * fields to it, retrieves the created JSON, and then calls 
      * RXS_DestroyJson() to clean up.
      *--------------------------------------------------------------
     H DFTACTGRP(*NO) BNDDIR('RXSBND') ACTGRP(*CALLER)

      /define RXSV6R1
      /copy QRPGLECPY,RXSCB

     D JSON            S                   Like(RXS_Var64Kv_t)

     D CreateJsonDS    DS                  LikeDS(RXS_CreateJsonDS_t)
     D RootDS          DS                  LikeDS(RXS_JsonStructureDS_t)
     D i               S              3U 0
      /free
        RXS_ResetDS( CreateJsonDS : RXS_DS_TYPE_CREATEJSON );
        RXS_ResetDS( RootDS : RXS_DS_TYPE_JSONSTRUCTURE );
        
        CreateJsonDS.JsonStructureType = RXS_JSON_STRUCTURE_ARRAY;
        RootDS = RXS_CreateJson( CreateJsonDS );

        for i = 1 to 5;
          RXS_ComposeJsonNull( *OMIT : RootDS );
        endfor;

        RXS_GetJsonString( JSON : CreateJsonDS );
        // JSON looks like:
        //
        // [null,null,null,null,null]

        RXS_DestroyJson( CreateJsonDS );

        *INLR = *ON;
      /end-free
```

## Data Structures

### RXS_JsonStructureDS_t

| Field | Description |
|---|---|
| `     D RXS_JsonStructureDS_t...      D                 DS                  Qualified Template Inz` |  |
| `     D   ReturnedErrorInfo...      D                                     LikeDS(RXS_ReturnedErrorInfoDS_t) Inz` |  |
| `     D   DataStructureType...      D                                5I 0 Inz(RXS_DS_TYPE_JSONSTRUCTURE)` | **Internal use only** |
| `     D   OnErrorMessageType...      D                                5I 0` |  |
| `     D   JsonStructureType...      D                                 N   Inz(RXS_JSON_STRUCTURE_OBJECT)` | **Internal use only** |
| `     D   JsonStructure@...      D                                 *   Inz(*Null)` | **Internal use only** |
| `     D   InputCcsid...      D                               10I 0 Inz(RXS_CCSID_JOB)` | Specifies the CCSID of the data being passed into the JSON composition subprocedures. Default is job CCSID. |
| `     D   OutputCcsid...      D                               10I 0 Inz(RXS_CCSID_JOB)` | Specifies the CCSID that the JSON will be output as from RXS_GetJsonString(). Default is job CCSID. |