While loading a fixture, don't set properties unless specifically in the load file.

[ghost]

I'm not really sure if this patch is correct, so take it with a grain of salt, but I was having an issue with a model like:

  public byte[] salt;
  public byte[] hashedPassword;


  void setPassword(String password) {
    // set salt and hashedPassword
  }

I could load a fixture:

User(ckent):
password: password

which would call the setPassword function through the BeanWrapper, but then the fields got cleared out by the pre-patch block (it sets each byte[] field, regardless if it is explicitly set in the yaml.) The new code only sets values if explicitly set.