visualization/visualization-model/src/main/java/se/jguru/nazgul/tools/visualization/model/diagram/Graph.java
public Edge addEdge(final String fromId, final String toId) {
        return getStatements().addEdge(fromId, toId, this);
    }
public Edge addEdge(final String fromId, final String toId) {
        return getStatements().addEdge(fromId, toId, this);
    }
Convenience method to add and return an Edge between a Node/Subgraph and another Node/Subgraph within the
immediate Statements in this Graph.

@param fromId The non-empty ID of the Node/Subgraph from which the Edge should originate.
@param toId   The non-empty ID of the Node/Subgraph to which the Edge should be directed.
@return The newly created Edge - or {@code null} if the Edge could not be created.