Are you filtering on this field?  I regularly have data fields that are blank or NULL appearing on reports.  If you are filtering on the field, you might try adding the condition that it is blank or null to be allowed to display.  In addition you might try changing how Crystal looks at the data....File/Options/Reporting, and place checks to Convert Null values to default.

One other thing to check.

Is your report using multiple tables? If yes, you'll want to verify that you are using either a left or right outter join opposed to an inner join between tables.

If you have multiple tables in a report they are commonly linked by a field that occurs in both tables.

For example if you have two tables joined by the "letter field"

Table 1    Table 2
A          A
B          B
C          C
D          

Inner join your report will display only those fields which occur in both tables (A,B and C)

Left Outter Join - report will display all records from table 1 and only those records from table 2 which match (A,B,C and D)

Right Outter join is the reverse will all records from table 2 and only those which match from Table 1.

The default linking in Crystal Reports is Inner Join. In needed, you can modify the type of join on the Links tab under the database expert.