Explain the Error in the Following $$\log _ { 3 } 2 + \log _ { 3 } \mathrm { M } = \log _ { 3 } ( 2 + \mathrm { M } )$$

Explain the error in the following: $$\log _ { 3 } 2 + \log _ { 3 } \mathrm { M } = \log _ { 3 } ( 2 + \mathrm { M } )$$