Merge pull request #61 from jszumski/master

Made the requirement of a non-nil formatName more explicit.

Author: mallorypaine

FastImageCache/FICImageCache.h

@@ -148,7 +148,7 @@ typedef void (^FICImageRequestCompletionBlock)(UIImage *sourceImage);
  
  @param entity The entity that uniquely identifies the source image.
  
- @param formatName The format name that uniquely identifies which image table to look in for the cached image.
+ @param formatName The format name that uniquely identifies which image table to look in for the cached image. Must not be nil.
  
  @param completionBlock The completion block that is called when the requested image is available or if an error occurs.
  
@@ -175,7 +175,7 @@ typedef void (^FICImageRequestCompletionBlock)(UIImage *sourceImage);
  
  @param entity The entity that uniquely identifies the source image.
  
- @param formatName The format name that uniquely identifies which image table to look in for the cached image.
+ @param formatName The format name that uniquely identifies which image table to look in for the cached image. Must not be nil.
  
  @param completionBlock The completion block that is called when the requested image is available or if an error occurs.
  

FastImageCache/FICImageCache.m

@@ -162,6 +162,8 @@ - (BOOL)asynchronouslyRetrieveImageForEntity:(id <FICEntity>)entity withFormatNa
 }
 
 - (BOOL)_retrieveImageForEntity:(id <FICEntity>)entity withFormatName:(NSString *)formatName loadSynchronously:(BOOL)loadSynchronously completionBlock:(FICImageCacheCompletionBlock)completionBlock {
+    NSParameterAssert(formatName);
+	
     BOOL imageExists = NO;
 
     FICImageTable *imageTable = [_imageTables objectForKey:formatName];