Fix simplejson incompatibility

qiskit_ibm_runtime/utils/json.py

@@ -319,6 +319,8 @@ class RuntimeDecoder(json.JSONDecoder):
     """JSON Decoder used by runtime service."""
 
     def __init__(self, *args: Any, **kwargs: Any):
+        if "encoding" in kwargs:
+            kwargs.pop("encoding")
         super().__init__(object_hook=self.object_hook, *args, **kwargs)
 
     def object_hook(self, obj: Any) -> Any:

release-notes/unreleased/1800.bug.rst

@@ -0,0 +1,2 @@
+Fixed an issue where users were unable to retrieve job results if 
+the python library ``simplejson`` was installed in their environment.

test/integration/test_job.py

@@ -46,6 +46,17 @@ def test_run_program(self, service):
         self.assertEqual(JobStatus.DONE, job.status())
         self.assertTrue(job.result())
 
+    @run_integration_test
+    def test_run_with_simplejson(self, service):
+        """Test retrieving job results with simplejson package installed."""
+        try:
+            __import__("simplejson")
+            job = self._run_program(service=service)
+            job.wait_for_final_state()
+            self.assertTrue(job.result())
+        except ImportError:
+            self.assertRaises(ImportError)
+
     @run_integration_test
     @quantum_only
     def test_run_program_log_level(self, service):