Merge pull request #1100 from jpfeuffer/fix/schemaVal_emptyDefaultStr

[FIX] Schema validation for empty string defaults

nf_core/schema.py

@@ -114,7 +114,8 @@ def sanitise_param_default(self, param):
 
         # For everything else, an empty string is an empty string
         if isinstance(param["default"], str) and param["default"].strip() == "":
-            return ""
+            param["default"] = ""
+            return param
 
         # Integers
         if param["type"] == "integer":