Conditions for a valid Red-Black Binary Search Tree

A red node can not have a red child.
The root node and all null nodes must always be black.
The path from the root node to every null leaf node must have the same amount of black nodes.

Example of a valid Red-Black Binary Search Tree

15-B, 8-R, 20-R, 2-B, 12-B, 17-B, 25-B, Null-B, Null-B, Null-B, Null-B, Null-B, Null-B, Null-B, Null-B