Fix a NPE in Performance tab when returning a Double object. (#503)
Fix a NPE in Performance tab when returning a Double object. (#503)

Check data availability and return Double.NAN when possible, avoid 
returning null.

Bug: N/A.
google/agi,google/agi,google/agi,google/agi,google/agi,google/agi,google/agi,google/agi