diff --git a/config/custom_schema_types.config b/config/custom_schema_types.config
index 2b1e117c..22c6b656 100644
--- a/config/custom_schema_types.config
+++ b/config/custom_schema_types.config
@@ -60,17 +60,17 @@ custom_schema_types {
     *   Check if given input is valid process list
     */
     check_if_process_list = { val, String name ->
-        if (!custom_schema_types.is_string(val)) {
+        if (custom_schema_types.is_string(val)) {
+            if (val.isEmpty()) {
+                throw new Exception("Empty string specified for ${name}. Please provide valid input.")
+            }
+        } else {
             try {
                 custom_schema_types.check_if_list(val, name)
             } catch(Exception e) {
                 throw new Exception("${name} should be either a string or a list. Please provide valid input.")
             }
         }
-
-        if (val.isEmpty()) {
-            throw new Exception("Empty string specified for ${name}. Please provide valid input.")
-        }
     }
 
     /**
diff --git a/config/default.config b/config/default.config
index 6d6909d8..f6dba7bf 100644
--- a/config/default.config
+++ b/config/default.config
@@ -7,7 +7,9 @@ params {
     cache_intermediate_pipeline_steps = false
 
     //max_number_of_parallel_jobs = 1
+    min_cpus   = 1
     max_cpus   = SysHelper.getAvailCpus()
+    min_memory = 1.MB
     max_memory = SysHelper.getAvailMemory()
 
     // default docker container registry