Add placeholder point in data set?

Question

I have five data sets that I'm throwing together in a ListLinePlot. Each data set corresponds to professor ratings per semester. One professor started a semester after everyone else. How do I add a placeholder point for Semester 1 so that their data is correctly placed? My code is below. Currently, I made profb's Semester 1 the same rating as Semester 2.

profa = {4.039, 3.588, 4.093, 3.722};
profb = {**3.733, 3.733**, 4.272, 4.118};
profc = {3.778, 3.626, 3.940, 4.425};
profd = {3.523, 3.837, 4.243, 3.995};
profe = {3.762, 3.575, 3.945, 4.210};

data = {profa, profb, profc, profd, profe};

dataplot = ListLinePlot[data,...]

If this question has been answered on another thread please direct me there! Thanks for your help.

Answer 1

In Mathematica, the convention is to replace missing data points with a call to Missing

profa = {4.039, 3.588, 4.093, 3.722};
profb = {Missing[], 3.733, 4.272, 4.118};
profc = {3.778, 3.626, 3.940, 4.425};
profd = {3.523, 3.837, 4.243, 3.995};
profe = {3.762, 3.575, 3.945, 4.210};
data = {profa, profb, profc, profd, profe};
dataplot = ListLinePlot[data]

Answer 2

This seems to work

profa = {4.039, 3.588, 4.093, 3.722};
profb = {Null, Null, 4.272, 4.118};
profc = {3.778, 3.626, 3.940, 4.425};
profd = {3.523, 3.837, 4.243, 3.995};
profe = {3.762, 3.575, 3.945, 4.210};
data = {profa, profb, profc, profd, profe};
dataplot = ListLinePlot[data]