code: public DataTable setOverwritePolicy(OverwritePolicy overwritePolicy) throws UnknownColumnException {
  		for (String attribute : overwritePolicy.getAttributeCodes()) {
  			assertAttributeExists(attribute);
  		}
  		this.overwritePolicy = overwritePolicy;
  		return this;
  	}
docs: Sets the overwrite policy to use with this table. If none is set,
  {@link OverwritePolicy#deleteNone()} is used.
  
  @param overwritePolicy the overwrite policy to use
  @return this table, to allow chaining
  @throws UnknownColumnException if any of the columns used in the policy
  doesn't exist in the table