diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Animation.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Animation.java
index 4ae99a0b0..2def4f12f 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Animation.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Animation.java
@@ -251,8 +251,9 @@ public class Animation {
 			frames = new float[frameCount << 1];
 		}
 
-		public void setBoneIndex (int boneIndex) {
-			this.boneIndex = boneIndex;
+		public void setBoneIndex (int index) {
+			if (index < 0) throw new IllegalArgumentException("index must be >= 0.");
+			this.boneIndex = index;
 		}
 
 		public int getBoneIndex () {
@@ -319,8 +320,9 @@ public class Animation {
 			frames = new float[frameCount * ENTRIES];
 		}
 
-		public void setBoneIndex (int boneIndex) {
-			this.boneIndex = boneIndex;
+		public void setBoneIndex (int index) {
+			if (index < 0) throw new IllegalArgumentException("index must be >= 0.");
+			this.boneIndex = index;
 		}
 
 		public int getBoneIndex () {
@@ -432,8 +434,9 @@ public class Animation {
 			frames = new float[frameCount * ENTRIES];
 		}
 
-		public void setSlotIndex (int slotIndex) {
-			this.slotIndex = slotIndex;
+		public void setSlotIndex (int index) {
+			if (index < 0) throw new IllegalArgumentException("index must be >= 0.");
+			this.slotIndex = index;
 		}
 
 		public int getSlotIndex () {
@@ -503,12 +506,13 @@ public class Animation {
 			return frames.length;
 		}
 
-		public int getSlotIndex () {
-			return slotIndex;
+		public void setSlotIndex (int index) {
+			if (index < 0) throw new IllegalArgumentException("index must be >= 0.");
+			this.slotIndex = index;
 		}
 
-		public void setSlotIndex (int slotIndex) {
-			this.slotIndex = slotIndex;
+		public int getSlotIndex () {
+			return slotIndex;
 		}
 
 		public float[] getFrames () {
@@ -660,8 +664,9 @@ public class Animation {
 			frameVertices = new float[frameCount][];
 		}
 
-		public void setSlotIndex (int slotIndex) {
-			this.slotIndex = slotIndex;
+		public void setSlotIndex (int index) {
+			if (index < 0) throw new IllegalArgumentException("index must be >= 0.");
+			this.slotIndex = index;
 		}
 
 		public int getSlotIndex () {
@@ -750,6 +755,7 @@ public class Animation {
 		}
 
 		public void setIkConstraintIndex (int index) {
+			if (index < 0) throw new IllegalArgumentException("index must be >= 0.");
 			this.ikConstraintIndex = index;
 		}
 
@@ -806,6 +812,7 @@ public class Animation {
 		}
 
 		public void setTransformConstraintIndex (int index) {
+			if (index < 0) throw new IllegalArgumentException("index must be >= 0.");
 			this.transformConstraintIndex = index;
 		}
 
@@ -874,6 +881,7 @@ public class Animation {
 		}
 
 		public void setPathConstraintIndex (int index) {
+			if (index < 0) throw new IllegalArgumentException("index must be >= 0.");
 			this.pathConstraintIndex = index;
 		}
 
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/AnimationStateData.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/AnimationStateData.java
index 84a2151f4..d0a806726 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/AnimationStateData.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/AnimationStateData.java
@@ -41,6 +41,7 @@ public class AnimationStateData {
 	float defaultMix;
 
 	public AnimationStateData (SkeletonData skeletonData) {
+		if (skeletonData == null) throw new IllegalArgumentException("skeletonData cannot be null.");
 		this.skeletonData = skeletonData;
 	}
 
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Bone.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Bone.java
index c454e1177..a8ae92eae 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Bone.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Bone.java
@@ -64,6 +64,7 @@ public class Bone implements Updatable {
 	 * @param parent May be null. */
 	public Bone (Bone bone, Skeleton skeleton, Bone parent) {
 		if (bone == null) throw new IllegalArgumentException("bone cannot be null.");
+		if (skeleton == null) throw new IllegalArgumentException("skeleton cannot be null.");
 		this.skeleton = skeleton;
 		this.parent = parent;
 		data = bone.data;
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/BoneData.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/BoneData.java
index ac8151445..821403b95 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/BoneData.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/BoneData.java
@@ -46,6 +46,7 @@ public class BoneData {
 
 	/** @param parent May be null. */
 	public BoneData (int index, String name, BoneData parent) {
+		if (index < 0) throw new IllegalArgumentException("index must be >= 0.");
 		if (name == null) throw new IllegalArgumentException("name cannot be null.");
 		this.index = index;
 		this.name = name;
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Event.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Event.java
index dcf57551e..e4730fbc9 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Event.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Event.java
@@ -39,6 +39,7 @@ public class Event {
 	final float time;
 
 	public Event (float time, EventData data) {
+		if (data == null) throw new IllegalArgumentException("data cannot be null.");
 		this.time = time;
 		this.data = data;
 	}
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/IkConstraint.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/IkConstraint.java
index d3710d08f..2c126492e 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/IkConstraint.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/IkConstraint.java
@@ -43,20 +43,22 @@ public class IkConstraint implements Updatable {
 	int bendDirection;
 
 	public IkConstraint (IkConstraintData data, Skeleton skeleton) {
+		if (data == null) throw new IllegalArgumentException("data cannot be null.");
+		if (skeleton == null) throw new IllegalArgumentException("skeleton cannot be null.");
 		this.data = data;
 		mix = data.mix;
 		bendDirection = data.bendDirection;
 
 		bones = new Array(data.bones.size);
-		if (skeleton != null) {
-			for (BoneData boneData : data.bones)
-				bones.add(skeleton.findBone(boneData.name));
-			target = skeleton.findBone(data.target.name);
-		}
+		for (BoneData boneData : data.bones)
+			bones.add(skeleton.findBone(boneData.name));
+		target = skeleton.findBone(data.target.name);
 	}
 
 	/** Copy constructor. */
 	public IkConstraint (IkConstraint constraint, Skeleton skeleton) {
+		if (constraint == null) throw new IllegalArgumentException("constraint cannot be null.");
+		if (skeleton == null) throw new IllegalArgumentException("skeleton cannot be null.");
 		data = constraint.data;
 		bones = new Array(constraint.bones.size);
 		for (Bone bone : constraint.bones)
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/IkConstraintData.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/IkConstraintData.java
index ef1bf0bc2..dfced65cc 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/IkConstraintData.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/IkConstraintData.java
@@ -41,6 +41,7 @@ public class IkConstraintData {
 	float mix = 1;
 
 	public IkConstraintData (String name) {
+		if (name == null) throw new IllegalArgumentException("name cannot be null.");
 		this.name = name;
 	}
 
@@ -57,6 +58,7 @@ public class IkConstraintData {
 	}
 
 	public void setTarget (BoneData target) {
+		if (target == null) throw new IllegalArgumentException("target cannot be null.");
 		this.target = target;
 	}
 
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/PathConstraint.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/PathConstraint.java
index f12f3c50c..7a59dab2c 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/PathConstraint.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/PathConstraint.java
@@ -16,6 +16,8 @@ public class PathConstraint implements Updatable {
 	final FloatArray lengths = new FloatArray(), positions = new FloatArray(), temp = new FloatArray();
 
 	public PathConstraint (PathConstraintData data, Skeleton skeleton) {
+		if (data == null) throw new IllegalArgumentException("data cannot be null.");
+		if (skeleton == null) throw new IllegalArgumentException("skeleton cannot be null.");
 		this.data = data;
 		position = data.position;
 		rotateMix = data.rotateMix;
@@ -31,6 +33,8 @@ public class PathConstraint implements Updatable {
 
 	/** Copy constructor. */
 	public PathConstraint (PathConstraint constraint, Skeleton skeleton) {
+		if (constraint == null) throw new IllegalArgumentException("constraint cannot be null.");
+		if (skeleton == null) throw new IllegalArgumentException("skeleton cannot be null.");
 		data = constraint.data;
 		bones = new Array(constraint.bones.size);
 		for (Bone bone : constraint.bones)
@@ -84,8 +88,7 @@ public class PathConstraint implements Updatable {
 
 		for (int i = 0; i < boneCount; i++) {
 			Bone bone = bones.get(i);
-			float length = bone.data.length;
-			float x = length * bone.a, y = length * bone.c;
+			float length = bone.data.length, x = length * bone.a, y = length * bone.c;
 			lengths.add((float)Math.sqrt(x * x + y * y));
 		}
 		float[] positions = computeWorldPositions(path, false);
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/PathConstraintData.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/PathConstraintData.java
index c4e4d4f03..6957c3716 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/PathConstraintData.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/PathConstraintData.java
@@ -11,6 +11,7 @@ public class PathConstraintData {
 	float offsetRotation;
 
 	public PathConstraintData (String name) {
+		if (name == null) throw new IllegalArgumentException("name cannot be null.");
 		this.name = name;
 	}
 
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Skeleton.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Skeleton.java
index 32ff7a6da..7d17cc563 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Skeleton.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Skeleton.java
@@ -303,6 +303,7 @@ public class Skeleton {
 
 	/** Sets the slots and the order they will be drawn. */
 	public void setDrawOrder (Array<Slot> drawOrder) {
+		if (drawOrder == null) throw new IllegalArgumentException("drawOrder cannot be null.");
 		this.drawOrder = drawOrder;
 	}
 
@@ -423,10 +424,12 @@ public class Skeleton {
 		return null;
 	}
 
-	/** Returns the axis aligned bounding box (AABB) of the region, mesh, and skinned mesh attachments for the current pose.
+	/** Returns the axis aligned bounding box (AABB) of the region and mesh attachments for the current pose.
 	 * @param offset The distance from the skeleton origin to the bottom left corner of the AABB.
 	 * @param size The width and height of the AABB. */
 	public void getBounds (Vector2 offset, Vector2 size) {
+		if (offset == null) throw new IllegalArgumentException("offset cannot be null.");
+		if (size == null) throw new IllegalArgumentException("size cannot be null.");
 		Array<Slot> drawOrder = this.drawOrder;
 		float minX = Integer.MAX_VALUE, minY = Integer.MAX_VALUE, maxX = Integer.MIN_VALUE, maxY = Integer.MIN_VALUE;
 		for (int i = 0, n = drawOrder.size; i < n; i++) {
@@ -458,6 +461,7 @@ public class Skeleton {
 
 	/** A convenience method for setting the skeleton color. The color can also be set by modifying {@link #getColor()}. */
 	public void setColor (Color color) {
+		if (color == null) throw new IllegalArgumentException("color cannot be null.");
 		this.color.set(color);
 	}
 
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonBinary.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonBinary.java
index a85630f9f..dfaf9ee32 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonBinary.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonBinary.java
@@ -89,6 +89,7 @@ public class SkeletonBinary {
 	}
 
 	public SkeletonBinary (AttachmentLoader attachmentLoader) {
+		if (attachmentLoader == null) throw new IllegalArgumentException("attachmentLoader cannot be null.");
 		this.attachmentLoader = attachmentLoader;
 	}
 
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonBounds.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonBounds.java
index 07831f211..7ff9d0f86 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonBounds.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonBounds.java
@@ -49,6 +49,7 @@ public class SkeletonBounds {
 	};
 
 	public void update (Skeleton skeleton, boolean updateAabb) {
+		if (skeleton == null) throw new IllegalArgumentException("skeleton cannot be null.");
 		Array<BoundingBoxAttachment> boundingBoxes = this.boundingBoxes;
 		Array<FloatArray> polygons = this.polygons;
 		Array<Slot> slots = skeleton.slots;
@@ -221,6 +222,7 @@ public class SkeletonBounds {
 
 	/** Returns the polygon for the specified bounding box, or null. */
 	public FloatArray getPolygon (BoundingBoxAttachment boundingBox) {
+		if (boundingBox == null) throw new IllegalArgumentException("boundingBox cannot be null.");
 		int index = boundingBoxes.indexOf(boundingBox, true);
 		return index == -1 ? null : polygons.get(index);
 	}
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonJson.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonJson.java
index 9e5f106a1..54dd11178 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonJson.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SkeletonJson.java
@@ -74,6 +74,7 @@ public class SkeletonJson {
 	}
 
 	public SkeletonJson (AttachmentLoader attachmentLoader) {
+		if (attachmentLoader == null) throw new IllegalArgumentException("attachmentLoader cannot be null.");
 		this.attachmentLoader = attachmentLoader;
 	}
 
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Slot.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Slot.java
index cac1e1644..f93478018 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Slot.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Slot.java
@@ -104,6 +104,7 @@ public class Slot {
 	}
 
 	public void setAttachmentVertices (FloatArray attachmentVertices) {
+		if (attachmentVertices == null) throw new IllegalArgumentException("attachmentVertices cannot be null.");
 		this.attachmentVertices = attachmentVertices;
 	}
 
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SlotData.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SlotData.java
index 1958251b3..eea1c6620 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SlotData.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/SlotData.java
@@ -42,6 +42,7 @@ public class SlotData {
 	BlendMode blendMode;
 
 	public SlotData (int index, String name, BoneData boneData) {
+		if (index < 0) throw new IllegalArgumentException("index must be >= 0.");
 		if (name == null) throw new IllegalArgumentException("name cannot be null.");
 		if (boneData == null) throw new IllegalArgumentException("boneData cannot be null.");
 		this.index = index;
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/TransformConstraint.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/TransformConstraint.java
index 171227ade..67858ab5e 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/TransformConstraint.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/TransformConstraint.java
@@ -12,20 +12,22 @@ public class TransformConstraint implements Updatable {
 	final Vector2 temp = new Vector2();
 
 	public TransformConstraint (TransformConstraintData data, Skeleton skeleton) {
+		if (data == null) throw new IllegalArgumentException("data cannot be null.");
+		if (skeleton == null) throw new IllegalArgumentException("skeleton cannot be null.");
 		this.data = data;
 		rotateMix = data.rotateMix;
 		translateMix = data.translateMix;
 		scaleMix = data.scaleMix;
 		shearMix = data.shearMix;
 
-		if (skeleton != null) {
-			bone = skeleton.findBone(data.bone.name);
-			target = skeleton.findBone(data.target.name);
-		}
+		bone = skeleton.findBone(data.bone.name);
+		target = skeleton.findBone(data.target.name);
 	}
 
 	/** Copy constructor. */
 	public TransformConstraint (TransformConstraint constraint, Skeleton skeleton) {
+		if (constraint == null) throw new IllegalArgumentException("constraint cannot be null.");
+		if (skeleton == null) throw new IllegalArgumentException("skeleton cannot be null.");
 		data = constraint.data;
 		bone = skeleton.bones.get(constraint.bone.data.index);
 		target = skeleton.bones.get(constraint.target.data.index);
diff --git a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/TransformConstraintData.java b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/TransformConstraintData.java
index 20d652603..4a20acd5b 100644
--- a/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/TransformConstraintData.java
+++ b/spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/TransformConstraintData.java
@@ -8,6 +8,7 @@ public class TransformConstraintData {
 	float offsetRotation, offsetX, offsetY, offsetScaleX, offsetScaleY, offsetShearY;
 
 	public TransformConstraintData (String name) {
+		if (name == null) throw new IllegalArgumentException("name cannot be null.");
 		this.name = name;
 	}
 
@@ -20,6 +21,7 @@ public class TransformConstraintData {
 	}
 
 	public void setBone (BoneData bone) {
+		if (bone == null) throw new IllegalArgumentException("bone cannot be null.");
 		this.bone = bone;
 	}
 
@@ -28,6 +30,7 @@ public class TransformConstraintData {
 	}
 
 	public void setTarget (BoneData target) {
+		if (target == null) throw new IllegalArgumentException("target cannot be null.");
 		this.target = target;
 	}