diff --git a/gcloud-java-storage/src/main/java/com/google/gcloud/storage/Storage.java b/gcloud-java-storage/src/main/java/com/google/gcloud/storage/Storage.java
index b35abbea8a88..ccbe121100e6 100644
--- a/gcloud-java-storage/src/main/java/com/google/gcloud/storage/Storage.java
+++ b/gcloud-java-storage/src/main/java/com/google/gcloud/storage/Storage.java
@@ -551,7 +551,7 @@ public Builder sourceOptions(Iterable<BlobSourceOption> options) {
       }
 
       /**
-       * Sets the copy target.
+       * Sets the copy target. Target blob information is copied from source.
        *
        * @return the builder.
        */
@@ -561,8 +561,9 @@ public Builder target(BlobId target) {
       }
 
       /**
-       * Sets the copy target and target options. Copied blob metadata is set to {@code target}.
-       * This method throws an exception if target blob's content type is {@code null}.
+       * Sets the copy target and target options. {@code target} parameter is used to override
+       * source blob information (e.g. {@code contentType}, {@code contentLanguage}), {@code
+       * target.contentType} is a required field.
        *
        * @return the builder.
        * @throws IllegalArgumentException if {@code target.contentType} is {@code null}
@@ -576,8 +577,9 @@ public Builder target(BlobInfo target, BlobTargetOption... options)
       }
 
       /**
-       * Sets the copy target and target options. Copied blob metadata is set to {@code target}.
-       * This method throws an exception if target blob's content type is {@code null}.
+       * Sets the copy target and target options. {@code target} parameter is used to override
+       * source blob information (e.g. {@code contentType}, {@code contentLanguage}), {@code
+       * target.contentType} is a required field.
        *
        * @return the builder.
        * @throws IllegalArgumentException if {@code target.contentType} is {@code null}
@@ -658,8 +660,9 @@ public Long megabytesCopiedPerChunk() {
     }
 
     /**
-     * Creates a copy request. Copied blob metadata is set to {@code target}. This method throws an
-     * exception if target blob's content type is {@code null}.
+     * Creates a copy request. {@code target} parameter is used to override source blob information
+     * (e.g. {@code contentType}, {@code contentLanguage}), {@code target.contentType} is a required
+     * field.
      *
      * @param sourceBucket name of the bucket containing the source blob
      * @param sourceBlob name of the source blob
@@ -674,8 +677,9 @@ public static CopyRequest of(String sourceBucket, String sourceBlob, BlobInfo ta
     }
 
     /**
-     * Creates a copy request. Copied blob metadata is set to {@code target}. This method throws an
-     * exception if target blob's content type is {@code null}.
+     * Creates a copy request. {@code target} parameter is used to override source blob information
+     * (e.g. {@code contentType}, {@code contentLanguage}), {@code target.contentType} is a required
+     * field.
      *
      * @param sourceBlobId a {@code BlobId} object for the source blob
      * @param target a {@code BlobInfo} object for the target blob
@@ -689,7 +693,7 @@ public static CopyRequest of(BlobId sourceBlobId, BlobInfo target)
     }
 
     /**
-     * Creates a copy request.
+     * Creates a copy request. Target blob information is copied from source.
      *
      * @param sourceBucket name of the bucket containing both the source and the target blob
      * @param sourceBlob name of the source blob
@@ -704,7 +708,7 @@ public static CopyRequest of(String sourceBucket, String sourceBlob, String targ
     }
 
     /**
-     * Creates a copy request.
+     * Creates a copy request. Target blob information is copied from source.
      *
      * @param sourceBucket name of the bucket containing the source blob
      * @param sourceBlob name of the source blob
@@ -716,7 +720,7 @@ public static CopyRequest of(String sourceBucket, String sourceBlob, BlobId targ
     }
 
     /**
-     * Creates a copy request.
+     * Creates a copy request. Target blob information is copied from source.
      *
      * @param sourceBlobId a {@code BlobId} object for the source blob
      * @param targetBlob name of the target blob, in the same bucket of the source blob
@@ -730,7 +734,7 @@ public static CopyRequest of(BlobId sourceBlobId, String targetBlob) {
     }
 
     /**
-     * Creates a copy request.
+     * Creates a copy request. Target blob information is copied from source.
      *
      * @param sourceBlobId a {@code BlobId} object for the source blob
      * @param targetBlobId a {@code BlobId} object for the target blob
@@ -748,9 +752,7 @@ public static Builder builder() {
     }
 
     private static void checkContentType(BlobInfo blobInfo) throws IllegalArgumentException {
-      if (blobInfo.contentType() == null) {
-        throw new IllegalArgumentException("Blob content type can not be null");
-      }
+      checkArgument(blobInfo.contentType() != null, "Blob content type can not be null");
     }
   }
 
diff --git a/gcloud-java-storage/src/test/java/com/google/gcloud/storage/CopyRequestTest.java b/gcloud-java-storage/src/test/java/com/google/gcloud/storage/CopyRequestTest.java
index febd74feb095..b7e8d14e53a1 100644
--- a/gcloud-java-storage/src/test/java/com/google/gcloud/storage/CopyRequestTest.java
+++ b/gcloud-java-storage/src/test/java/com/google/gcloud/storage/CopyRequestTest.java
@@ -126,4 +126,4 @@ public void testCopyRequestOfStringFail() {
     Storage.CopyRequest.of(
         SOURCE_BUCKET_NAME, SOURCE_BLOB_NAME, BlobInfo.builder(TARGET_BLOB_ID).build());
   }
-}
\ No newline at end of file
+}