issue #698 add fallback situations

openeo/rest/connection.py

@@ -1068,7 +1068,7 @@ def describe_process(self, id: str, namespace: Optional[str] = None) -> dict:
 
     def get_schema_from_process_parameter(
         self, process_id: str, parameter_id: str, namespace: Optional[str] = None
-    ) -> dict:
+    ) -> Union[dict, list]:
         """
         Returns schema of the parameter of the process from the back end.
 
@@ -2123,6 +2123,4 @@ def search_list_for_dict_key(lst: list, key: str) -> Union[dict, list]:
                 result = item[key]
             else:
                 raise OpenEoClientException("Multiple keys found with value {v}.".format(v=key))
-    if result is None:
-        raise OpenEoClientException("No dictionary found with the key {k}.".format(k=key))
     return result

openeo/rest/datacube.py

@@ -2724,8 +2724,13 @@ def sar_backscatter(
         .. versionadded:: 0.4.9
         .. versionchanged:: 0.4.10 replace `orthorectify` and `rtc` arguments with `coefficient`.
         """
-        schema = self.connection.get_schema_from_process_parameter("sar_backscatter", "coefficient")
-        coefficient_options = search_list_for_dict_key(schema, "enum")
+        if self.connection == None:
+            coefficient_options = [None]
+        else:
+            schema = self.connection.get_schema_from_process_parameter("sar_backscatter", "coefficient")
+            coefficient_options = search_list_for_dict_key(schema, "enum")
+            if coefficient_options is None:
+                coefficient_options = [None]
         if coefficient not in coefficient_options:
             raise OpenEoClientException("Invalid `sar_backscatter` coefficient {c!r}. Should be one of {o}".format(
                 c=coefficient, o=coefficient_options