Unable to see the X-axis bin range value for Histogram chart for list of 20 values

chart data range--> =Sheet1!$A$2:$A$21   

above red marked value should show the range --> [0.02.0.02]

 instead of []. 

if we changed the value from 0.02 to 0.05 for all 20 values. then showing bin range [0.05,0.5].  so why for 0.02 related value not showed in x-axis.  how to fix this issue. Quick help is appreciated..

 i believed that it is bug. if not why bin range not showed when value is same for last 20 times.