ENH: F remove value or property

Summary

Precondition for https://gitlab.indiscale.com/caosdb/customers/geomar/management/-/issues/110. Adds a function that removes a value from a property, and optionally, the property from the entity if it is empty afterwards. We used to implement this functionality in several customer-specific extensions, so I think it makes sense to have this upstream.

Focus

Check whether the behavior of the new function is reasonable also in the corner cases of list properties in which the value to be removed occurs more than once (i.e., remove "a" from ["a", "b", "a"]) and in case of an already empty property (remove "something" from None vs remove None from None).

Test Environment

Unit tests should be sufficient, but feel free to test it manually, too. Also check whether the docstring is understandable.

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• Reference related issues
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src/caosdb/common/models.py

@@ -458,10 +458,10 @@ class Entity:
 
         Do nothing if this entity does not have a property of this
         ``property_name`` or if the property value is different of the given
-        ``value``. By default, the property is removed form this entity if it is
-        empty (i.e., value=None) after removal of the value. This behavior can
-        be changed by setting ``remove_if_empty_afterwards`` to ``False`` in which
-        case the property remains.
+        ``value``. By default, the property is removed from this entity if it
+        becomes empty (i.e., value=None) through removal of the value. This
+        behavior can be changed by setting ``remove_if_empty_afterwards`` to
+        ``False`` in which case the property remains.
 
         Notes
         -----
@@ -469,29 +469,34 @@ class Entity:
         than once in this list, only its first occurrance is deleted (similar
         to the behavior of Python's ``list.remove()``.)
 
-        If the property is already empty and a value != None is to be removed,
-        the property is not removed afterwards even if
-        ``remove_if_empty_afterwards`` is set to ``True`` (the property being
-        empty is not an effect of calling this function).
+        If the property was empty (prop.value == None) before, the property is
+        not removed afterwards even if ``remove_if_empty_afterwards`` is set to
+        ``True``.  Rationale: the property being empty is not an effect of
+        calling this function.
 
         Parameters
         ----------
         property_name : str
             Name of the property from which the ``value`` will be removed.
+
         value
             Value that is to be removed.
+
         remove_if_empty_afterwards : bool, optional
-            Whether the property is to be removed from this entity if it is
+            Whether the property shall be removed from this entity if it is
             emptied by removing the ``value``. Default is ``True``.
 
         Returns
         -------
         self
             This entity.
+
         """
 
         if self.get_property(property_name) is None:
             return self
+        if self.get_property(property_name).value is None:
+            remove_if_empty_afterwards = False
         empty_afterwards = False
         if isinstance(self.get_property(property_name).value, list):
             if value in self.get_property(property_name).value: