Add error message hint for special case issue

Author: BrianMichell

src/mdio/builder/dataset_builder.py

@@ -232,6 +232,15 @@ def add_variable(  # noqa: PLR0913
             raise ValueError(msg)
         if dimensions is None or not dimensions:
             msg = "'dimensions' must be a non-empty list"
+            if name == "trace_mask":  # coverage: exclude
+                msg += (
+                    "Error occurred while adding special case variable `trace_mask`."
+                    "This is likely an issue with how a custom template has been defined."
+                    "Please check the documentation https://github.com/TGSAI/mdio-python/issues/718 "
+                    "for more information."
+                    # TODO(Anybody): Update the link to point to the appropriate documentation when it is available.
+                    # https://github.com/TGSAI/mdio-python/issues/718
+                )
             raise ValueError(msg)
 
         # Validate that the variable is not already defined