docs(path): document slice bound clamping and null path arguments

pages/advanced-algorithms/available-algorithms/path.mdx

@@ -44,7 +44,7 @@ node-relationship-node order.
 
 {<h4 className="custom-header"> Input: </h4>}
 
-- `path: Path` ➡ The given path.
+- `path: Path` ➡ The given path. If `null`, the function returns `null`.
 
 {<h4 className="custom-header"> Output: </h4>}
 
@@ -78,8 +78,10 @@ paths can't be combined.
 
 {<h4 className="custom-header"> Input: </h4>}
 
-- `first: Path` ➡ The first path.
-- `second: Path` ➡ The second path.
+- `first: Path` ➡ The first path. If `null`, the function returns the second path.
+- `second: Path` ➡ The second path. If `null`, the function returns the first path.
+
+If both paths are `null`, the function returns `null`.
 
 {<h4 className="custom-header"> Output: </h4>}
 
@@ -114,14 +116,26 @@ The function returns a subpath of the given path.
 
 {<h4 className="custom-header"> Input: </h4>}
 
-- `path: Path` ➡ The given path.
-- `offset: int = 0` ➡ The first node index from the given path to be included in the subpath.
-- `length: int = -1` ➡ Length of the subpath. If set to -1 the subpath will end on the final node of the given path.
+- `path: Path` ➡ The given path. If `null`, the function returns `null`.
+- `offset: int = 0` ➡ The first node index from the given path to be included in
+  the subpath. A negative offset is read as `0`, and an offset past the end of
+  the given path starts the subpath at its final node.
+- `length: int = -1` ➡ Length of the subpath. If set to -1 the subpath will end
+  on the final node of the given path. A length reaching past the end of the
+  given path ends the subpath on its final node, and any other negative length
+  returns a subpath with no relationships.
 
 {<h4 className="custom-header"> Output: </h4>}
 
 - `Path` ➡ The subpath of the given path.
 
+<Callout type="info">
+An offset or length outside the given path is adjusted to the nearest subpath
+rather than raising an error, so bounds computed from an expression such as
+`length(path)` can be passed without guarding them first. The shortest subpath
+the function returns is a single node.
+</Callout>
+
 {<h4 className="custom-header"> Usage: </h4>}
 
 Use the following query to return a subpath of the given path:
@@ -143,6 +157,27 @@ The result is returned in shortened form with () signifying nodes and [] signify
 +------------------------------------------------------------------------------------------------------+
 ```
 
+Use the following query to see how bounds outside the given path are adjusted:
+
+```cypher
+MATCH path = (:Node1)-[:CONNECTED*4]->(:Node5)
+RETURN path.slice(path, -5, 2) AS negative_offset,
+       path.slice(path, 10, -1) AS offset_past_end,
+       path.slice(path, 1, -3) AS negative_length;
+```
+
+The negative offset starts the subpath at the first node, the offset past the
+end returns the final node on its own, and the negative length returns a
+subpath with no relationships:
+
+```plaintext
++--------------------------------------------------------+--------------------------------------------------------+--------------------------------------------------------+
+| negative_offset                                        | offset_past_end                                        | negative_length                                        |
++--------------------------------------------------------+--------------------------------------------------------+--------------------------------------------------------+
+| (:Node1)-[:CONNECTED]->(:Node2)-[:CONNECTED]->(:Node3) | (:Node5)                                               | (:Node2)                                               |
++--------------------------------------------------------+--------------------------------------------------------+--------------------------------------------------------+
+```
+
 ## Procedures
 
 ### `create()`