Add more assertions.

Author: slembcke

cocos2d/CCNode.m

@@ -1727,6 +1727,7 @@ -(CCShader *)shader
 
 -(void)setShader:(CCShader *)shader
 {
+	NSAssert(shader, @"CCNode.shader cannot be nil.");
 	_shader = shader;
 	_renderState = nil;
 }
@@ -1768,6 +1769,7 @@ -(NSMutableDictionary *)shaderUniforms
 
 -(void)setBlendMode:(CCBlendMode *)blendMode
 {
+	NSAssert(blendMode, @"CCNode.blendMode cannot be nil.");
 	if(_blendMode != blendMode){
 		_blendMode = blendMode;
 		_renderState = nil;

cocos2d/CCRendererBasicTypes.m

@@ -309,6 +309,10 @@ -(instancetype)initWithBlendMode:(CCBlendMode *)blendMode shader:(CCShader *)sha
 -(instancetype)initWithBlendMode:(CCBlendMode *)blendMode shader:(CCShader *)shader shaderUniforms:(NSDictionary *)shaderUniforms copyUniforms:(BOOL)copyUniforms
 {
 	if((self = [super init])){
+		NSAssert(blendMode, @"CCRenderState: Blending mode is nil");
+		NSAssert(shader, @"CCRenderState: Shader is nil");
+		NSAssert(shaderUniforms, @"CCRenderState: shader uniform dictionary is nil.");
+		
 		_blendMode = blendMode;
 		_shader = shader;
 		_shaderUniforms = (copyUniforms ? [shaderUniforms copy] : shaderUniforms);