[1.12]Opening a Gui referencing to another Guis' object

Hello, it's me again with another Problem on my GUI.
The Custom Buttons I made get a Card Attribute to save the Card that they are related to.
I wanted to use this in order to construct a new GUI, which is opened when the Player clicks a Card Button.
Then I would use this Card as a Parameter in the new GUI, in order to create a Card-Info-File from the data stored in the buttons' Card Attribute.
The Problem is that when I open the new Gui, the old one gets closed and all the objects I was referencing seem to then equal null, which is why I get a NullPointerException when I try using the cards' data...
Is there a good way to do this? I tried cloning the Card but that wouldn't work either. Then I tried to find out which Card I have to create by comparing the buttons' Card to the Cards the Player owns, and then using the one
which is found in the playerCards Array. I will just Show you my GUI-Code, although it is a bit messy, it should still be possible to understand it.
 

package armamenthaki.duelmonsters.gui;

import java.util.ArrayList;
import java.util.Collection;

import armamenthaki.duelmonsters.DuelMonsters;
import armamenthaki.duelmonsters.duel.Card;
import armamenthaki.duelmonsters.duel.cards.CardSpeedWarrior;
import armamenthaki.duelmonsters.individual.capabilities.DuelDataProvider;
import armamenthaki.duelmonsters.util.Log;
import net.minecraft.client.Minecraft;
import net.minecraft.client.gui.GuiButton;
import net.minecraft.client.gui.GuiScreen;
import net.minecraft.client.gui.ScaledResolution;
import net.minecraft.client.renderer.GlStateManager;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.util.ResourceLocation;
import net.minecraftforge.client.event.RenderGameOverlayEvent;
import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;

public class GuiDeckEditor extends GuiScreen
{
	//the cards I want to display in the boxes
    private ArrayList<Card> deck = new ArrayList<Card>();
	private ArrayList<Card> displayedCards = new ArrayList<Card>();
	//the players cards which out of which the the displayedCards resolves
	private ArrayList<Card> playerCards = new ArrayList<Card>();
	
	//the background, fixed to the screen width and height
	private static final ResourceLocation debase = new ResourceLocation("duelmonsters", "textures/textures/gui/guidebase.png");
	private ButtonCard clickedButton;
	private int allCardButtons;
	private EntityPlayer theplayer;
	public ResourceLocation guiresource;
	private ScaledResolution res;
	private int scroll;
	private int scroll2;
	private boolean scrollingUp;
	private boolean scrollingDown;
	private int buttonHeight;
	
    //controls up and down for both boxes
	private ButtonControl cardUp;
	private ButtonControl cardDown;
	private ButtonControl deckUp;
	private ButtonControl deckDown;
	
	public GuiDeckEditor(EntityPlayer player)
	{
		
		theplayer = player;
		if(!player.world.isRemote)
		{
			//capabilities don't seem to be working as the gui is cient side
			Log.logString("player");
			playerCards = player.getCapability(DuelDataProvider.DUELDAT_CAP, null).getPlayerCards();
			playerCards.add(new CardSpeedWarrior());
		}
		//just some cards to add to the screen for testing purposes
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		displayedCards.add(new CardSpeedWarrior());
		
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());
		deck.add(new CardSpeedWarrior());


		this.mc = Minecraft.getMinecraft();
		res = new ScaledResolution(this.mc);
		


	}
	/* basic Gui methods*/
	@Override
    public void drawScreen(int mouseX, int mouseY, float partialTicks)
	{

		initializeStuff(mouseX, mouseY);
		drawBackAndForeground();
	}

	@Override
    public void initGui()
    {
		initDisplayedCards();
		initDeckCards();
		initControls();
    }
	
	/*this happens in drawScreen*/
	public void drawBackAndForeground()
	{
		GlStateManager.pushMatrix();
		float x = (float)width/512;
		float y = (float)height/288;
		int a = res.getScaleFactor();
		mc.renderEngine.bindTexture(debase);
		GlStateManager.scale(x, y, 1.0);
		GlStateManager.translate(0F, 0F, 2F);
		this.drawModalRectWithCustomSizedTexture(0, 0, 0, 0, 512, 288, 512, 288);
		GlStateManager.popMatrix();	
	}
	
	public void initializeStuff(int mouseX, int mouseY)
	{
		int i = this.buttonList.size()-1;
		for(; i>=0; i--)
		{
			if(this.buttonList.get(i) instanceof ButtonCard)
			{
				this.buttonList.remove(i);
			}
		}
		this.initDisplayedCards();
		this.initDeckCards();
		if(cardUp.dragging)++scroll;
		if(cardDown.dragging)--scroll;
		if(deckUp.dragging)++scroll2;
		if(deckDown.dragging)--scroll2;
		this.updateControlResources(mouseX, mouseY);
		cardUp.drawButton(mc);
		cardDown.drawButton(mc);
		deckUp.drawButton(mc);
		deckDown.drawButton(mc);
		for(GuiButton button : this.buttonList)
		{
			if(button instanceof ButtonCard)
			{
				((ButtonCard) button).drawScreen(mc);
			}
		}
	}
	
	/*responds to user input*/
	@Override
	public void actionPerformed(GuiButton button)
	{	
		if(button.id <= allCardButtons && cardUp.hoverState != 1 && cardDown.hoverState != 1)
		{
			for(Card card : playerCards)
			{
				//this tests if the resourcePath of any players' card equals the buttons' resource, which would mean that they would be the same cards.
				//however, the capabilities don't work..
				if(card.getResource().getResourcePath()==(((ButtonCard) button).getResource().getResourcePath()))
				{
					mc.displayGuiScreen(new GuiCardDisplay(this, card));
					Log.logString("okokok");
				}
			}
		}
		if(button.id == allCardButtons+1)
		{
			cardUp.dragging = true;
		}
		if(button.id == allCardButtons+2)
		{
			cardDown.dragging = true;
		}
		if(button.id == allCardButtons+3)
		{
			deckUp.dragging = true;
		}
		if(button.id == allCardButtons+4)
		{
			deckDown.dragging = true;
		}
		
		
	}
	/*get and set*/
	public int getWidth()
	{
		return this.width;
	}
	public int getHeight()
	{
		return this.height;
	}
	
	/*init for all buttons*/
	public void initDisplayedCards()
	{
		int line = 0;
		int column = 0;
		int id = 0;
		for(Card itCard : displayedCards) 
		{
			ResourceLocation resource = itCard.getResource();
			int i = width/6 + (column* width/17);
			int j = (height/6+height/30) + (line* width/13)+this.scroll;
			float trX = (float)width/6 +(float)(column* width/17);
			float trY = (float)(height/6+height/30) +(float)(line* width/13)+(float)this.scroll;
			float sf = (float)width/256F /20F;
			int rF = res.getScaleFactor();
			float fWidth = sf * 256F;
			float fHeight = sf * 373F;
			int bWidth = (int)fWidth;
			int bHeight = (int)fHeight;
			this.buttonHeight = bHeight;
	        column++;
	        if(column == 5)
	        {
	        	line++;
				column = 0;
	        }
			GuiButton button = new ButtonCard(id, sf, i, j, "", itCard, trX, trY, bWidth, bHeight, this);
			this.buttonList.add(button);
			id++;
		}
		allCardButtons = id;
	}
	
	
	public void initDeckCards()
	{
		int line = 0;
		int column = 0;
		int id = allCardButtons;
		for(Card itCard : deck) 
		{
			ResourceLocation resource = itCard.getResource();
			float trX = (float)width-(float)width/2.45F +(float)(column* width/17);
			float trY = (float)height/3.1F +(float)(line* width/13)+(float)this.scroll2;
			int i = (int)trX;
			int j = (int)trY;
			float sf = (float)width/256F /20F;
			int rF = res.getScaleFactor();
			float fWidth = sf * 256F;
			float fHeight = sf * 373F;
			int bWidth = (int)fWidth;
			int bHeight = (int)fHeight;
			this.buttonHeight = bHeight;
	        column++;
	        if(column == 5)
	        {
	        	line++;
				column = 0;
	        }
			GuiButton button = new ButtonCard(id, sf, i, j, "", itCard, trX, trY, bWidth, bHeight, this);
			this.buttonList.add(button);
			id++;
		}
		allCardButtons = id;
	}
	public void initControls()
	{
		initButtonUp();
		initButtonDown();
		initDeckUp();
		initDeckDown();
	}
	
	//init controls
	public void initButtonUp()
	{
		ResourceLocation resource = new ResourceLocation(DuelMonsters.MODID, "textures/textures/gui/buttonUp.png");
		float sF = (float)width/33F/20;
		int posX = width/4 + width/27;
		int posY = height/8;
		float fWidth =  sF * 33F;
		float fHeight = sF * 19F;
		int bWidth = (int)fWidth;
		int bHeight = (int)fHeight;
		ButtonControl cardUp = new ButtonControl(allCardButtons+1, posX, posY, bWidth, bHeight, "", resource);
		cardUp.setScale(sF);
		cardUp.setTextureScale(33, 19);
		cardUp.setTr((float)posX, (float)posY);
		this.cardUp = cardUp;
		this.buttonList.add(this.cardUp);
	}
	
	public void initButtonDown()
	{
		ResourceLocation resource = new ResourceLocation(DuelMonsters.MODID, "textures/textures/gui/buttonDown.png");
		float sF = (float)width/33F/20;
		int posX = width/4 + width/27;
		int posY = height-height/16;
		float fWidth =  sF * 33F;
		float fHeight = sF * 19F;
		int bWidth = (int)fWidth;
		int bHeight = (int)fHeight;
		ButtonControl cardDown = new ButtonControl(allCardButtons+2, posX, posY, bWidth, bHeight, "", resource);
		cardDown.setScale(sF);
		cardDown.setTextureScale(33, 19);
		cardDown.setTr((float)posX, (float)posY);
		this.cardDown = cardDown;
		this.buttonList.add(this.cardDown);
	}
	
	public void initDeckUp()
	{
		ResourceLocation resource = new ResourceLocation(DuelMonsters.MODID, "textures/textures/gui/buttonUp.png");
		float sF = (float)width/33F/20;
		int posX = width-width/4;
		int posY = height/4;
		float fWidth =  sF * 33F;
		float fHeight = sF * 19F;
		int bWidth = (int)fWidth;
		int bHeight = (int)fHeight;
		ButtonControl cardUp = new ButtonControl(allCardButtons+3, posX, posY, bWidth, bHeight, "", resource);
		cardUp.setScale(sF);
		cardUp.setTextureScale(33, 19);
		cardUp.setTr((float)posX, (float)posY);
		this.deckUp = cardUp;
		this.buttonList.add(this.deckUp);
	}
	
	public void initDeckDown()
	{
		ResourceLocation resource = new ResourceLocation(DuelMonsters.MODID, "textures/textures/gui/buttonDown.png");
		float sF = (float)width/33F/20;
		int posX = width-width/4;
		int posY = height-height/16;
		float fWidth =  sF * 33F;
		float fHeight = sF * 19F;
		int bWidth = (int)fWidth;
		int bHeight = (int)fHeight;
		ButtonControl cardDown = new ButtonControl(allCardButtons+4, posX, posY, bWidth, bHeight, "", resource);
		cardDown.setScale(sF);
		cardDown.setTextureScale(33, 19);
		cardDown.setTr((float)posX, (float)posY);
		this.deckDown = cardDown;
		this.buttonList.add(this.deckDown);
	}
	
	public void updateControlResources(int mouseX, int mouseY)
	{
		cardUp.setMouse(mouseX, mouseY);
		cardDown.setMouse(mouseX, mouseY);
		deckUp.setMouse(mouseX, mouseY);
		deckDown.setMouse(mouseX, mouseY);
		if(cardUp.hoverState == 1)cardUp.setResource(new ResourceLocation(DuelMonsters.MODID, "textures/textures/gui/buttonup2.png"));
		else cardUp.setResource(new ResourceLocation(DuelMonsters.MODID, "textures/textures/gui/buttonup.png"));
		if(cardDown.hoverState == 1)cardDown.setResource(new ResourceLocation(DuelMonsters.MODID, "textures/textures/gui/buttondown2.png"));
		else cardDown.setResource(new ResourceLocation(DuelMonsters.MODID, "textures/textures/gui/buttondown.png"));
		if(deckUp.hoverState == 1)deckUp.setResource(new ResourceLocation(DuelMonsters.MODID, "textures/textures/gui/buttonup2.png"));
		else deckUp.setResource(new ResourceLocation(DuelMonsters.MODID, "textures/textures/gui/buttonup.png"));
		if(deckDown.hoverState == 1)deckDown.setResource(new ResourceLocation(DuelMonsters.MODID, "textures/textures/gui/buttondown2.png"));
		else deckDown.setResource(new ResourceLocation(DuelMonsters.MODID, "textures/textures/gui/buttondown.png"));
	}
	
}

And this is the Gui I am opening:

package armamenthaki.duelmonsters.gui;

import java.util.ArrayList;

import armamenthaki.duelmonsters.duel.Card;
import net.minecraft.client.gui.GuiButton;
import net.minecraft.client.gui.GuiScreen;
import net.minecraft.client.renderer.GlStateManager;
import net.minecraft.util.ResourceLocation;

public class GuiCardDisplay extends GuiScreen
{
	
	private ResourceLocation resource;
	private GuiScreen guiIn;
	private Card card;
	
	public GuiCardDisplay(GuiScreen gui, Card card)
	{
		this.card = card;
		this.resource = card.getResource();
		this.guiIn = gui;
	}
	
	
	public GuiCardDisplay(GuiScreen gui, ArrayList<Card> cards, int id)
	{
		this.card = cards.get(id);
		this.resource = card.getResource();
		this.guiIn = gui;
	}
	@Override
	public void drawScreen(int mouseX, int mouseY, float partialTicks)
	{
		mc.renderEngine.bindTexture(resource);
		GlStateManager.translate((float)this.width/4, (float)this.height/3, 1.0);
		float sf = (float)this.width/256F/4F;
		GlStateManager.scale(sf, sf, 1.0F);
		this.drawModalRectWithCustomSizedTexture(0, 0, 0, 0, 256, 373, 256, 373);
	}
	
	@Override
	public void initGui()
	{
		GuiButton button = new GuiButton(0, 0, 0, this.width, this.height, "");
		this.buttonList.add(button);
	}
	
	public void actionPerformed(GuiButton button)
	{
		if(button.id == 0)mc.displayGuiScreen(this.guiIn);
	}
}

I hope it isn't to hard to understand, thank you for your help.