Allow all parts of state to be undefined

This prevents type errors when calling setState.

src/components/tree/tree.tsx

@@ -93,9 +93,9 @@ export interface TreeComponentPropsFromState {
 }
 
 export interface TreeComponentState {
-  hoveredNode: ReactTreeNode | null
-  tree: PhyloTree | null
-  treeToo: PhyloTree | null
+  hoveredNode?: ReactTreeNode
+  tree?: PhyloTree
+  treeToo?: PhyloTree
   geneSortFn?: any
   selectedNode?: Record<string, never>  // I think this is ReactTreeNode but only set to empty.
 }
@@ -116,11 +116,7 @@ export class TreeComponent extends React.Component<TreeComponentProps, TreeCompo
       secondTree: null
     };
     this.tangleRef = undefined;
-    this.state = {
-      hoveredNode: null,
-      tree: null,
-      treeToo: null
-    };
+    this.state = {};
 
     /* bind callbacks */
     this.clearSelectedNode = callbacks.clearSelectedNode.bind(this);