message: doc(runtime-c-api) Rephrase null pointers.
diff: @@ -135,7 +135,7 @@ pub extern "C" fn wasmer_memory_grow(memory: *mut wasmer_memory_t, delta: u32) -
  /// Reads the current length (in pages) of the given memory.
  ///
  -/// The function returns zero if `memory` is null.
  +/// The function returns zero if `memory` is a null pointer.
  ///
  /// Example:
  ///
  @@ -160,7 +160,7 @@ pub extern "C" fn wasmer_memory_length(memory: *const wasmer_memory_t) -> u32 {
  /// Gets a pointer to the beginning of the contiguous memory data
  /// bytes.
  ///
  -/// The function returns `NULL` if `memory` is NULL.
  +/// The function returns `NULL` if `memory` is a null pointer.
  ///
  /// Note that when the memory grows, it can be reallocated, and thus
  /// the returned pointer can be invalidated.
  @@ -189,7 +189,7 @@ pub extern "C" fn wasmer_memory_data(memory: *const wasmer_memory_t) -> *mut u8
  /// Gets the size in bytes of the memory data.
  ///
  -/// This function returns 0 if `memory` is NULL.
  +/// This function returns 0 if `memory` is a null pointer.
  ///
  /// Example:
  ///
  