Why is nitrogen gas released when diazo compounds form carbenes?

When diazo compounds are used as precursors to form carbenes, the release of nitrogen gas is a direct result of the chemical cleavage of the diazo group.

These compounds contain a diazo group, which consists of two nitrogen atoms joined to each other and to a carbon atom by a double bond. When these molecules are subjected to photolysis (treatment with light) or pyrolysis (treatment with heat), the bond between the carbon and the nitrogen atoms breaks. This decomposition process causes the diazo group to split, yielding the corresponding carbene and a free molecule of nitrogen gas as a byproduct.1