Regarding the function $f ( x ) = \sin x + \frac { 1 } { \sin x }$ , there are four propositions:
(1) The graph of $f ( x )$ is symmetric about the $y$-axis.
(2) The graph of $f ( x )$ is symmetric about the origin.
(3) The graph of $f ( x )$ is symmetric about the line $x = \frac { \pi } { 2 }$ .
(4) The minimum value of $f ( x )$ is 2 .
The sequence numbers of all true propositions are $\_\_\_\_$ .