diff --git a/src/main/java/com/raoulvdberge/refinedstorage/container/ContainerBase.java b/src/main/java/com/raoulvdberge/refinedstorage/container/ContainerBase.java
index 26b5668c7..0be5b740e 100755
--- a/src/main/java/com/raoulvdberge/refinedstorage/container/ContainerBase.java
+++ b/src/main/java/com/raoulvdberge/refinedstorage/container/ContainerBase.java
@@ -11,6 +11,8 @@ import net.minecraft.inventory.Slot;
 import net.minecraft.item.ItemStack;
 import net.minecraftforge.items.ItemHandlerHelper;
 
+import javax.annotation.Nonnull;
+
 public abstract class ContainerBase extends Container {
     private TileBase tile;
     private EntityPlayer player;
@@ -58,7 +60,7 @@ public abstract class ContainerBase extends Container {
         Slot slot = id >= 0 ? getSlot(id) : null;
 
         if (slot instanceof SlotFilter) {
-            if (((SlotFilter) slot).isWithSize()) {
+            if (((SlotFilter) slot).allowsSize()) {
                 if (clickType == ClickType.QUICK_MOVE) {
                     slot.putStack(ItemStack.EMPTY);
                 } else if (!player.inventory.getItemStack().isEmpty()) {
@@ -106,14 +108,14 @@ public abstract class ContainerBase extends Container {
     protected ItemStack mergeItemStackToSpecimen(ItemStack stack, int begin, int end) {
         for (int i = begin; i < end; ++i) {
             if (API.instance().getComparer().isEqualNoQuantity(getStackFromSlot(getSlot(i)), stack)) {
-                return null;
+                return ItemStack.EMPTY;
             }
         }
 
         for (int i = begin; i < end; ++i) {
             Slot slot = getSlot(i);
 
-            if (getStackFromSlot(slot) == null && slot.isItemValid(stack)) {
+            if (getStackFromSlot(slot).isEmpty() && slot.isItemValid(stack)) {
                 slot.putStack(ItemHandlerHelper.copyStackWithSize(stack, 1));
                 slot.onSlotChanged();
 
@@ -124,6 +126,7 @@ public abstract class ContainerBase extends Container {
         return ItemStack.EMPTY;
     }
 
+    @Nonnull
     private ItemStack getStackFromSlot(Slot slot) {
         ItemStack stackInSlot = slot.getStack();
 
diff --git a/src/main/java/com/raoulvdberge/refinedstorage/container/ContainerInterface.java b/src/main/java/com/raoulvdberge/refinedstorage/container/ContainerInterface.java
index 61dec6702..3be521156 100755
--- a/src/main/java/com/raoulvdberge/refinedstorage/container/ContainerInterface.java
+++ b/src/main/java/com/raoulvdberge/refinedstorage/container/ContainerInterface.java
@@ -17,7 +17,7 @@ public class ContainerInterface extends ContainerBase {
         }
 
         for (int i = 0; i < 9; ++i) {
-            addSlotToContainer(new SlotFilter(tile.getExportSpecimenItems(), i, 8 + (18 * i), 54, SlotFilter.SPECIMEN_SIZE));
+            addSlotToContainer(new SlotFilter(tile.getExportSpecimenItems(), i, 8 + (18 * i), 54, SlotFilter.FILTER_ALLOW_SIZE));
         }
 
         for (int i = 0; i < 9; ++i) {
diff --git a/src/main/java/com/raoulvdberge/refinedstorage/container/ContainerProcessingPatternEncoder.java b/src/main/java/com/raoulvdberge/refinedstorage/container/ContainerProcessingPatternEncoder.java
index 95e880445..0ef22e6d7 100755
--- a/src/main/java/com/raoulvdberge/refinedstorage/container/ContainerProcessingPatternEncoder.java
+++ b/src/main/java/com/raoulvdberge/refinedstorage/container/ContainerProcessingPatternEncoder.java
@@ -22,7 +22,7 @@ public class ContainerProcessingPatternEncoder extends ContainerBase {
         int y = 20;
 
         for (int i = 0; i < 9 * 2; ++i) {
-            addSlotToContainer(new SlotFilter(encoder.getConfiguration(), i, x, y, SlotFilter.SPECIMEN_SIZE));
+            addSlotToContainer(new SlotFilter(encoder.getConfiguration(), i, x, y, SlotFilter.FILTER_ALLOW_SIZE));
 
             x += 18;
 
diff --git a/src/main/java/com/raoulvdberge/refinedstorage/container/slot/SlotFilter.java b/src/main/java/com/raoulvdberge/refinedstorage/container/slot/SlotFilter.java
index 22c50402e..ceec67bbe 100755
--- a/src/main/java/com/raoulvdberge/refinedstorage/container/slot/SlotFilter.java
+++ b/src/main/java/com/raoulvdberge/refinedstorage/container/slot/SlotFilter.java
@@ -15,8 +15,8 @@ import javax.annotation.Nonnull;
 import java.lang.reflect.Field;
 
 public class SlotFilter extends SlotItemHandler {
-    public static final int SPECIMEN_SIZE = 1;
-    public static final int SPECIMEN_BLOCK = 2;
+    public static final int FILTER_ALLOW_SIZE = 1;
+    public static final int FILTER_ALLOW_BLOCKS = 2;
 
     private int flags = 0;
 
@@ -38,7 +38,7 @@ public class SlotFilter extends SlotItemHandler {
     @Override
     public boolean isItemValid(@Nonnull ItemStack stack) {
         if (super.isItemValid(stack)) {
-            if (isBlockOnly()) {
+            if (allowsBlocks()) {
                 return stack.getItem() instanceof ItemBlock || stack.getItem() instanceof ItemBlockSpecial || stack.getItem() instanceof IPlantable || stack.getItem() instanceof ItemSkull;
             }
 
@@ -50,19 +50,19 @@ public class SlotFilter extends SlotItemHandler {
 
     @Override
     public void putStack(@Nonnull ItemStack stack) {
-        if (!stack.isEmpty() && !isWithSize()) {
+        if (!stack.isEmpty() && !allowsSize()) {
             stack.setCount(1);
         }
 
         super.putStack(stack);
     }
 
-    public boolean isWithSize() {
-        return (flags & SPECIMEN_SIZE) == SPECIMEN_SIZE;
+    public boolean allowsSize() {
+        return (flags & FILTER_ALLOW_SIZE) == FILTER_ALLOW_SIZE;
     }
 
-    public boolean isBlockOnly() {
-        return (flags & SPECIMEN_BLOCK) == SPECIMEN_BLOCK;
+    public boolean allowsBlocks() {
+        return (flags & FILTER_ALLOW_BLOCKS) == FILTER_ALLOW_BLOCKS;
     }
 
     public static IBlockState getBlockState(IBlockAccess world, BlockPos pos, ItemStack stack) {
diff --git a/src/main/java/com/raoulvdberge/refinedstorage/container/slot/SlotFilterType.java b/src/main/java/com/raoulvdberge/refinedstorage/container/slot/SlotFilterType.java
index a58176976..bfc5c353b 100755
--- a/src/main/java/com/raoulvdberge/refinedstorage/container/slot/SlotFilterType.java
+++ b/src/main/java/com/raoulvdberge/refinedstorage/container/slot/SlotFilterType.java
@@ -26,13 +26,13 @@ public class SlotFilterType extends SlotFilter {
     }
 
     @Override
-    public boolean isWithSize() {
-        return super.isWithSize() && type.getType() != IType.FLUIDS;
+    public boolean allowsSize() {
+        return super.allowsSize() && type.getType() != IType.FLUIDS;
     }
 
     @Override
-    public boolean isBlockOnly() {
-        return super.isBlockOnly() && type.getType() == IType.ITEMS;
+    public boolean allowsBlocks() {
+        return super.allowsBlocks() && type.getType() == IType.ITEMS;
     }
 
     @Override