If you are making an API Request, post the Request here.
In order for someone to help you with API Request questions, it is critical that you post here the API Request you are using.
Remember to replace your Key with [MY_KEY].

oops, sorry.. there goes Request{method=GET, url=https://api.themoviedb.org/3/movie/popular?api_key=MY_KEY

Post here the Request you are using to get crew and cast with Movie ID.

I can't get to that request as movie id returned in previous response is null...

Something like this for every record:

> adult = "false"
> backdrop_path = "/lDycwBLtLAVzLMK5nUvuf01DYCr.jpg"
> castAndCrew = null
> genre_ids = {ArrayList@12120}  size = 4
> **id = null**
> original_language = "en"
> original_title = "Double Dragon"
> overview = "Set 15 years in the future in post-earthquake California, where San Diego and Los Angeles are merged into one city, two teenage brothers have half of a powerful ancient Chinese talisman. An evil gang leader named Bo Abobo has the other half, and determines to get the brothers' half and have a complete medallion so he can gain absolute power of the magical Double Dragon medallion."
> popularity = "5.126"
> poster = null
> poster_path = "/yv21myb4k32qUhuEmuCg1uYiOOC.jpg"
> release_date = "1994-11-04"
> title = "Double Dragon"
> video = "false"
> vote_average = "4"
> vote_count = "107"
> shadow$_klass_ = {Class@11053} "class com.tmdb.myapp.model.MovieList"
> shadow$_monitor_ = -2051063459

For the example response you posted I can deduce that you are using a third party APP.
Am I right?

A normal TMDb response looks like this:
https://api.themoviedb.org/3/movie/2436?api_key=[MY_KEY]&language=en-US&append_to_response=credits

{
  "adult": false,
  "backdrop_path": "/lDycwBLtLAVzLMK5nUvuf01DYCr.jpg",
  "belongs_to_collection": null,
  "budget": 3500000,
  "genres": [
    {
      "id": 28,
      "name": "Action"
    },
    {
      "id": 12,
      "name": "Adventure"
    },
    {
      "id": 35,
      "name": "Comedy"
    },
    {
      "id": 878,
      "name": "Science Fiction"
    }
  ],
  "homepage": null,
  "id": 2436,
  "imdb_id": "tt0106761",
  "original_language": "en",
  "original_title": "Double Dragon",
  "overview": "Set 15 years in the future in post-earthquake California, where San Diego and Los Angeles are merged into one city, two teenage brothers have half of a powerful ancient Chinese talisman. An evil gang leader named Bo Abobo has the other half, and determines to get the brothers' half and have a complete medallion so he can gain absolute power of the magical Double Dragon medallion.",
  "popularity": 5.126,
  "poster_path": "/yv21myb4k32qUhuEmuCg1uYiOOC.jpg",
  "production_companies": [
    {
      "id": 37,
      "logo_path": "/nlG4JEjJ7SAFDehgIVvHFBPW23y.png",
      "name": "Gramercy Pictures",
      "origin_country": "US"
    }
  ],
  "production_countries": [
    {
      "iso_3166_1": "US",
      "name": "United States of America"
    }
  ],
  "release_date": "1994-11-04",
  "revenue": 2341309,
  "runtime": 89,
  "spoken_languages": [
    {
      "iso_639_1": "en",
      "name": "English"
    },
    {
      "iso_639_1": "fr",
      "name": "Français"
    }
  ],
  "status": "Released",
  "tagline": "Power. Justice. Darkness. Light.",
  "title": "Double Dragon",
  "video": false,
  "vote_average": 4,
  "vote_count": 107,
  "credits": {
    "cast": [
      {
        "cast_id": 21,
        "character": "Kongo Shuko",
        "credit_id": "52fe4357c3a36847f804cf11",
        "gender": 2,
        "id": 418,
        "name": "Robert Patrick",
        "order": 0,
        "profile_path": "/dpUIbzLpExv69faSRyww8A4ydxf.jpg"
      },
      {
        "cast_id": 22,
        "character": "Jimmy Lee",
        "credit_id": "52fe4357c3a36847f804cf15",
        "gender": 2,
        "id": 18702,
        "name": "Mark Dacascos",
        "order": 1,
        "profile_path": "/rPVgMthfpUpPAsHj5RRS0Gk0mHM.jpg"
      },
      {
        "cast_id": 23,
        "character": "Billy Lee",
        "credit_id": "52fe4357c3a36847f804cf19",
        "gender": 2,
        "id": 24965,
        "name": "Scott Wolf",
        "order": 2,
        "profile_path": "/y5NBlTvKDIe2csxZeeYv6ooM8rN.jpg"
      },
      {
        "cast_id": 24,
        "character": "Linda Lash",
        "credit_id": "52fe4357c3a36847f804cf1d",
        "gender": 1,
        "id": 24966,
        "name": "Kristina Wagner",
        "order": 3,
        "profile_path": "/5xUGgz4kJkAzi52rwkHXtDtB7Wz.jpg"
      },
      {
        "cast_id": 25,
        "character": "Satori Imada",
        "credit_id": "52fe4357c3a36847f804cf21",
        "gender": 1,
        "id": 16578,
        "name": "Julia Nickson",
        "order": 4,
        "profile_path": "/zQzqbbfixENqr2NLp92EOtL7POQ.jpg"
      },
      {
        "cast_id": 26,
        "character": "Marian Delario",
        "credit_id": "52fe4357c3a36847f804cf25",
        "gender": 1,
        "id": 24967,
        "name": "Alyssa Milano",
        "order": 5,
        "profile_path": "/6M5BxJoF7oZl50lnEo4rYG2K7G8.jpg"
      },
      {
        "cast_id": 27,
        "character": "Bo Abodo 1",
        "credit_id": "52fe4357c3a36847f804cf29",
        "gender": 2,
        "id": 24968,
        "name": "Nils Allen Stewart",
        "order": 6,
        "profile_path": "/qeTM6yMFJeP9dhudYGAKduzaoGD.jpg"
      },
      {
        "cast_id": 28,
        "character": "Bo Abodo 2",
        "credit_id": "52fe4357c3a36847f804cf2d",
        "gender": 2,
        "id": 24969,
        "name": "Henry Kingi",
        "order": 7,
        "profile_path": "/7NfbNpe2PQZI5BcdvBxAfVfmroi.jpg"
      },
      {
        "cast_id": 29,
        "character": "Smartass Mohawk",
        "credit_id": "52fe4357c3a36847f804cf31",
        "gender": 2,
        "id": 24970,
        "name": "John Asher",
        "order": 8,
        "profile_path": null
      },
      {
        "cast_id": 30,
        "character": "Lewis",
        "credit_id": "52fe4357c3a36847f804cf35",
        "gender": 2,
        "id": 61704,
        "name": "Al Leong",
        "order": 9,
        "profile_path": "/imOF8DbaIQ7HENiSAZsNWEQ3MiY.jpg"
      },
      {
        "cast_id": 31,
        "character": "Huey",
        "credit_id": "52fe4357c3a36847f804cf39",
        "gender": 2,
        "id": 169628,
        "name": "Jeff Imada",
        "order": 10,
        "profile_path": "/sUNSaNQreSHYaJvKr0SfiBqMPDV.jpg"
      },
      {
        "cast_id": 32,
        "character": "Maniac Leader",
        "credit_id": "52fe4357c3a36847f804cf3d",
        "gender": 2,
        "id": 7073,
        "name": "Michael Berryman",
        "order": 11,
        "profile_path": "/kqIQo7IqpW5DLcMmWD7mkxokyLX.jpg"
      },
      {
        "cast_id": 33,
        "character": "Herself",
        "credit_id": "52fe4357c3a36847f804cf41",
        "gender": 1,
        "id": 97752,
        "name": "Vanna White",
        "order": 12,
        "profile_path": "/1N5aGcOf65DgNNy7eE1zhxPbfNo.jpg"
      },
      {
        "cast_id": 35,
        "character": "Himself",
        "credit_id": "596edf05c3a3687fc7019aec",
        "gender": 2,
        "id": 43120,
        "name": "Andy Dick",
        "order": 13,
        "profile_path": "/ebNRu8oV7Ifv5aoP23UyNnx0lZS.jpg"
      }
    ],
    "crew": [
      {
        "credit_id": "52fe4357c3a36847f804cea1",
        "department": "Writing",
        "gender": 2,
        "id": 24949,
        "job": "Screenplay",
        "name": "Michael Davis",
        "profile_path": "/s4u26Oo2fUqFc1ZwFqo4y8Hmh67.jpg"
      },
      {
        "credit_id": "52fe4357c3a36847f804cead",
        "department": "Writing",
        "gender": 2,
        "id": 24951,
        "job": "Screenplay",
        "name": "Peter Gould",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804ceb3",
        "department": "Production",
        "gender": 1,
        "id": 3182,
        "job": "Producer",
        "name": "Jane Hamsher",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804ceb9",
        "department": "Production",
        "gender": 2,
        "id": 3183,
        "job": "Producer",
        "name": "Don Murphy",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804cebf",
        "department": "Production",
        "gender": 2,
        "id": 24952,
        "job": "Producer",
        "name": "Alan Schechter",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804cec5",
        "department": "Production",
        "gender": 2,
        "id": 24953,
        "job": "Producer",
        "name": "Ash R. Shah",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804cecb",
        "department": "Sound",
        "gender": 0,
        "id": 24954,
        "job": "Original Music Composer",
        "name": "Jay Ferguson",
        "profile_path": "/39MWXPmJT8dp2qALFlCAFLBzQkd.jpg"
      },
      {
        "credit_id": "52fe4357c3a36847f804ced1",
        "department": "Sound",
        "gender": 0,
        "id": 24955,
        "job": "Original Music Composer",
        "name": "Tolga Katas",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804ced7",
        "department": "Camera",
        "gender": 2,
        "id": 24956,
        "job": "Director of Photography",
        "name": "Gary B. Kibbe",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804cedd",
        "department": "Editing",
        "gender": 0,
        "id": 24957,
        "job": "Editor",
        "name": "Florent Retz",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804cee3",
        "department": "Production",
        "gender": 1,
        "id": 13674,
        "job": "Casting",
        "name": "Annette Benson",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804cee9",
        "department": "Production",
        "gender": 1,
        "id": 24958,
        "job": "Casting",
        "name": "Harriet Greenspan",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804ceef",
        "department": "Art",
        "gender": 2,
        "id": 11423,
        "job": "Art Direction",
        "name": "Mayne Berke",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804cef5",
        "department": "Art",
        "gender": 0,
        "id": 24959,
        "job": "Art Direction",
        "name": "Maya Shimoguchi",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804cefb",
        "department": "Art",
        "gender": 0,
        "id": 24960,
        "job": "Set Decoration",
        "name": "Kristan Andrews",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804cf01",
        "department": "Costume & Make-Up",
        "gender": 0,
        "id": 24961,
        "job": "Costume Design",
        "name": "Fiona Spence",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804cf07",
        "department": "Costume & Make-Up",
        "gender": 0,
        "id": 24962,
        "job": "Makeup Artist",
        "name": "Teri Blythe",
        "profile_path": null
      },
      {
        "credit_id": "52fe4357c3a36847f804cf0d",
        "department": "Crew",
        "gender": 0,
        "id": 24963,
        "job": "Special Effects",
        "name": "Terry Erickson",
        "profile_path": null
      },
      {
        "credit_id": "58b3fcde92514177b801503e",
        "department": "Directing",
        "gender": 2,
        "id": 22636,
        "job": "Director",
        "name": "James Yukich",
        "profile_path": null
      }
    ]
  }
}

o_O... I'm using retrofit lib...

Sorry but I can not help.
The problem must be in the retrofit programming.
A good place to ask for help is on stackoverflow.com

ok, thanks anyways...