public Matrix3f set(Matrix3f matrix) {
        if (null == matrix) {
            loadIdentity();
        } else {
            m00 = matrix.m00;
            m01 = matrix.m01;
            m02 = matrix.m02;
            m10 = matrix.m10;
            m11 = matrix.m11;
            m12 = matrix.m12;
            m20 = matrix.m20;
            m21 = matrix.m21;
            m22 = matrix.m22;
        }
        return this;
    }
Copies the matrix argument. If the argument is null, the current instance
is set to identity (diagonals = 1, other elements = 0).

@param matrix the matrix to copy (unaffected) or null for identity
@return the (modified) current instance (for chaining)
jme3-core/src/main/java/com/jme3/math/Matrix3f.java