Workaround "empty paragraph" warning with clang -Wdocumentation

Eigen/src/Core/util/Constants.h

@@ -56,8 +56,8 @@ const int HugeCost = 10000;
   * for a matrix, this means that the storage order is row-major.
   * If this bit is not set, the storage order is column-major.
   * For an expression, this determines the storage order of
-  * the matrix created by evaluation of that expression. 
-  * \sa \ref TopicStorageOrders */
+  * the matrix created by evaluation of that expression.
+  * \sa \blank  \ref TopicStorageOrders */
 const unsigned int RowMajorBit = 0x1;
 
 /** \ingroup flags
@@ -168,7 +168,7 @@ const unsigned int NestByRefBit = 0x100;
   * can be either row-major or column-major.
   * The precise choice will be decided at evaluation time or when
   * combined with other expressions.
-  * \sa \ref RowMajorBit, \ref TopicStorageOrders */
+  * \sa \blank  \ref RowMajorBit, \ref TopicStorageOrders */
 const unsigned int NoPreferredStorageOrderBit = 0x200;
 
 /** \ingroup flags

Eigen/src/Core/util/Memory.h

@@ -784,7 +784,7 @@ template<typename T> void swap(scoped_array<T> &a,scoped_array<T> &b)
 * std::map< int, Vector3f > my_map_vec3;
 * \endcode
 *
-* \sa \ref TopicStlContainers.
+* \sa \blank \ref TopicStlContainers.
 */
 template<class T>
 class aligned_allocator : public std::allocator<T>

Eigen/src/Core/util/XprHelper.h

@@ -29,7 +29,7 @@ typedef EIGEN_DEFAULT_DENSE_INDEX_TYPE DenseIndex;
 /**
  * \brief The Index type as used for the API.
  * \details To change this, \c \#define the preprocessor symbol \c EIGEN_DEFAULT_DENSE_INDEX_TYPE.
- * \sa \ref TopicPreprocessorDirectives, StorageIndex.
+ * \sa \blank \ref TopicPreprocessorDirectives, StorageIndex.
  */
 
 typedef EIGEN_DEFAULT_DENSE_INDEX_TYPE Index;