Test for textX dependency in self-check

fixes #2592

Author: sebix

CHANGELOG.md

@@ -37,6 +37,7 @@ Please refer to the [NEWS](NEWS.md) for a list of changes which have an affect o
 - `intelmq.bots.experts.fake.expert`:
   - Use database path matching to installation type (PR#2606 by Sebastian Wagner).
   - Add new mode `random_single_value` (PR#2601 by Sebastian Wagner).
+- `intelmq.bots.experts.sieve.expert`: Test for textX dependency in self-check (PR#2605 by Sebastian Wagner).
 
 #### Outputs
 

intelmq/bots/experts/sieve/expert.py

@@ -83,6 +83,9 @@ def check(parameters):
 
             metamodel = None
 
+            if metamodel_from_file is None:
+                raise MissingDependencyError("textx")
+
             try:
                 metamodel = metamodel_from_file(grammarfile)
             except TextXError as e: