-- vec_elements with null LHS
SELECT vec_elements(NULL::text[], '{1,2,3}'::int[]);
 vec_elements 
--------------
 
(1 row)

-- vec_elements with null RHS
SELECT vec_elements('{a,b,c}'::text[], NULL);
 vec_elements 
--------------
 
(1 row)

-- vec_elements with both null
SELECT vec_elements(NULL::text[], NULL);
 vec_elements 
--------------
 
(1 row)

-- vec_elements with negative index
SELECT vec_elements('{a,b,c}'::text[], '{-1,2,3}'::int[]);
ERROR:  vec_elements indices can't be less than 1, but got -1
-- vec_elements with zero index
SELECT vec_elements('{a,b,c}'::text[], '{0,2,3}'::int[]);
ERROR:  vec_elements indices can't be less than 1, but got 0
-- vec_elements with too-large index
SELECT vec_elements('{a,b,c}'::text[], '{1,2,4}'::int[]);
 vec_elements 
--------------
 {a,b,NULL}
(1 row)

-- vec_elements with same index twice
SELECT vec_elements('{a,b,c}'::text[], '{1,2,2}'::int[]);
 vec_elements 
--------------
 {a,b,b}
(1 row)

-- vec_elements with normal indexes
SELECT vec_elements('{a,b,c}'::text[], '{1,2,3}'::int[]);
 vec_elements 
--------------
 {a,b,c}
(1 row)

-- vec_elements with normal indexes backwards
SELECT vec_elements('{a,b,c}'::text[], '{3,2,1}'::int[]);
 vec_elements 
--------------
 {c,b,a}
(1 row)

-- vec_elements with empty array on LHS
SELECT vec_elements('{}'::text[], '{1,2,3}'::int[]);
   vec_elements   
------------------
 {NULL,NULL,NULL}
(1 row)

-- vec_elements with empty array on RHS
SELECT vec_elements('{a,b,c}'::text[], '{}'::int[]);
 vec_elements 
--------------
 {}
(1 row)