Sets the receiver's line dash style to the argument. The default
value is <code>null</code>. If the argument is not <code>null</code>,
the receiver's line style is set to <code>SWT.LINE_CUSTOM</code>, otherwise
it is set to <code>SWT.LINE_SOLID</code>.
@param dashes the dash style to be used for drawing lines
@exception IllegalArgumentException <ul>
<li>ERROR_INVALID_ARGUMENT - if any of the values in the array is less than or equal 0</li>
</ul>
@exception SWTException <ul>
<li>ERROR_GRAPHIC_DISPOSED - if the receiver has been disposed</li>
</ul>
Sets the receiver's line dash style to the argument. The default value is <code>null</code>. If the argument is not <code>null</code>, the receiver's line style is set to <code>SWT.LINE_CUSTOM</code>, otherwise it is set to <code>SWT.LINE_SOLID</code>.
@param dashes the dash style to be used for drawing lines
@exception IllegalArgumentException <ul> <li>ERROR_INVALID_ARGUMENT - if any of the values in the array is less than or equal 0</li> </ul> @exception SWTException <ul> <li>ERROR_GRAPHIC_DISPOSED - if the receiver has been disposed</li> </ul>
@since 3.1