API response using Retrofit returns null for certain parameters which aren't null

I am using Retrofit for my android application, but few of the parameters come back as null while others have values, it's working fine on POSTMAN.

Function I'm using for Api Call:

private fun apiCall(search: String): List<SortedApiData> {

    var recyclerDataList: List<SortedApiData> = ArrayList<SortedApiData>()

    val consumer = OkHttpOAuthConsumer("9c6c751a78db41b9a8bec92ef28c7656", "3f302d7930a74c1db0304ce675d4d41b")
    consumer.setTokenWithSecret("","")

    val client1 = OkHttpClient.Builder()
        .addInterceptor(SigningInterceptor(consumer))
        .build()

    var retrofit : Retrofit = Retrofit.Builder()
        .baseUrl(BaseUrl)
        .client(client1)
        .addConverterFactory(GsonConverterFactory.create())
        .build()

    val api: Client = retrofit.create(Client::class.java)
    val call: retrofit2.Call<ApiData?>? = api.getResponse(search, 5, 0, 0)

    call?.enqueue(object : Callback<ApiData?> {
        override fun onFailure(call: retrofit2.Call<ApiData?>, t: Throwable?) {
            Log.v("retrofit", t.toString())
        }

        override fun onResponse(call: retrofit2.Call<ApiData?>, response: Response<ApiData?>) {
            val data: ApiData? = response.body()
            popUprecycler.visibility = View.VISIBLE

            Log.v("retrofit", data.toString())

            recyclerDataList = createList(data)
            adapter = PopUpAdapter(this@PopPage, recyclerDataList)
            popUprecycler.layoutManager = GridLayoutManager(applicationContext, 2)
            popUprecycler.itemAnimator = DefaultItemAnimator()
            popUprecycler.setHasFixedSize(true)
            popUprecycler.adapter = adapter
            Log.i("Shrey", "shit")
        }
})
    return recyclerDataList
}

@GET Request function:

interface Client {

    @GET("{id}/icons")
    fun getResponse(@Path("id") id: String?,@Query("limit") limit: Int?,@Query("offset") offset: Int?,@Query("page") page: Int?): Call<ApiData?>?
}

Model class:

public class ApiData{
    private int total;
    private String generatedAt;
    private Collection collection;
    private List<IconsItem> icons;

    public int getTotal(){
        return total;
    }

    public String getGeneratedAt(){
        return generatedAt;
    }

    public Collection getCollection(){
        return collection;
    }

    public List<IconsItem> getIcons(){
        return icons;
    }
}

Icon Model Class:

public class IconsItem{
    private Sponsor sponsor;
    private String uploaderId;
    private String isActive;
    private String nounjiFree;
    private int year;
    private String dateUploaded;
    private Object sponsorCampaignLink;
    private int termId;
    private String sponsorId;
    private String termSlug;
    private String licenseDescription;
    private List<TagsItem> tags;
    private String attributionPreviewUrl;
    private String updatedAt;
    private String previewUrl;
    private Uploader uploader;
    private String attribution;
    private String previewUrl42;
    private String freemium;
    private String term;
    private String id;
    private String permalink;
    private String isExplicit;
    private String previewUrl84;

    public Sponsor getSponsor(){
        return sponsor;
    }

    public String getUploaderId(){
        return uploaderId;
    }

    public String getIsActive(){
        return isActive;
    }

    public String getNounjiFree(){
        return nounjiFree;
    }

    public int getYear(){
        return year;
    }

    public String getDateUploaded(){
        return dateUploaded;
    }

    public Object getSponsorCampaignLink(){
        return sponsorCampaignLink;
    }

    public int getTermId(){
        return termId;
    }

    public String getSponsorId(){
        return sponsorId;
    }

    public String getTermSlug(){
        return termSlug;
    }

    public String getLicenseDescription(){
        return licenseDescription;
    }

    public List<TagsItem> getTags(){
        return tags;
    }

    public String getAttributionPreviewUrl(){
        return attributionPreviewUrl;
    }

    public String getUpdatedAt(){
        return updatedAt;
    }

    public String getPreviewUrl(){
        return previewUrl;
    }

    public Uploader getUploader(){
        return uploader;
    }

    public String getAttribution(){
        return attribution;
    }

    public String getPreviewUrl42(){
        return previewUrl42;
    }

    public String getFreemium(){
        return freemium;
    }

    public String getTerm(){
        return term;
    }

    public String getId(){
        return id;
    }

    public String getPermalink(){
        return permalink;
    }

    public String getIsExplicit(){
        return isExplicit;
    }

    public String getPreviewUrl84(){
        return previewUrl84;
    }
}

API response notice the highlighted value which shouldn't be null:

The correct API response :