replace IdIsNull trait with associated fn (#156)

src/_macros.rs

@@ -259,6 +259,11 @@ macro_rules! impl_id_traits {
         impl $idtype {
             /// NULL value for this type.
             pub const NULL: $idtype = Self($crate::TSK_NULL);
+
+            /// Return `true` is `self == Self::NULL`
+            pub fn is_null(&self) -> bool {
+                *self == Self::NULL
+            }
         }
 
         impl From<$crate::tsk_id_t> for $idtype {
@@ -267,12 +272,6 @@ macro_rules! impl_id_traits {
             }
         }
 
-        impl $crate::IdIsNull for $idtype {
-            fn is_null(&self) -> bool {
-                self.0 == Self::NULL
-            }
-        }
-
         impl From<$idtype> for usize {
             fn from(value: $idtype) -> Self {
                 value.0 as usize

src/lib.rs

@@ -220,7 +220,6 @@ pub use node_table::{NodeTable, NodeTableRow};
 pub use population_table::{PopulationTable, PopulationTableRow};
 pub use site_table::{SiteTable, SiteTableRow};
 pub use table_collection::TableCollection;
-pub use traits::IdIsNull;
 pub use traits::NodeListGenerator;
 pub use traits::TableAccess;
 pub use traits::TskitTypeAccess;

src/test_simplification.rs

@@ -2,7 +2,6 @@
 mod tests {
     use crate::test_fixtures::make_small_table_collection_two_trees;
     use crate::test_fixtures::treeseq_from_small_table_collection_two_trees;
-    use crate::IdIsNull;
     use crate::NodeId;
     use crate::SimplificationOptions;
     use crate::TableAccess;

src/traits.rs

@@ -200,7 +200,3 @@ pub trait NodeListGenerator: TableAccess {
         self.nodes().create_node_id_vector(f)
     }
 }
-
-pub trait IdIsNull {
-    fn is_null(&self) -> bool;
-}