SSRS and null datetime - reporting-services

Question

I always thought that when a stored procedure brought back a null datetime that an SSRS report would show mindate in that cell. The thing is, in my experience this is not always true. I can't figure out why. Sometimes a report will show blank and sometimes mindate for a null datetime. Why is that?
Is there rules or documentation (that makes sense) that explains how this works? It's hard to be consistent when the tools you are using are not consistent. I can make two reports that are set up exactly the same way. One will show mindate and one will show blank for null datetimes. I don't get it.
EDIT:
First of all, yes the mindate thing has happened to many.
https://www.google.com/search?num=50&q=ssrs+null+date+show+blank&oq=ssrs+null+date+show+blank&gs_l=serp.3...8759.9774.0.9941.10.10.0.0.0.0.152.888.8j2.10.0....0...1c.1.25.serp..8.2.166.kl2WBVx4Ijw
Almost every result has someone talking about the mindate when they want a blank. Many of the results are from Stack Overflow so before you start telling me it never happens, realize you are flat wrong. You may have never seen it. I have never seen a severed finger in my food in all my years of eating and thousands of meals. Doesn't mean it hasn't happened to someone.....
Example of one that is showing min date:
In the report the expression for the text box is:
=Fields!SecondaryInjuryRecordDate.Value
The number formatting was set to Date->01/31/2000 in the placeholder properties window.
Pretty straightforward, nothing weird going on there. RIGHT?
In the proc, the code for that column is:
CASE WHEN ISNULL(l.SecondaryInjury, 0) = 0 THEN '' ELSE l.SecondaryInjuryDXDate END AS SecondaryInjuryRecordDate
That resulted in mindate being shown whenever SecondaryInjuryDXDate was null. I had to switch to this:
CASE WHEN ISNULL(l.SecondaryInjury, 0) = 0 THEN '' ELSE ISNULL(l.SecondaryInjuryDXDate, '') END AS SecondaryInjuryRecordDate
...to get blanks when the date was null.
SecondaryInjuryDXDate is a DATETIME and
SecondaryInjury is a bit.

Answer 1

Within SSRS, by default a NULL DateTime value will be represented as an empty string instead.
If data formatting is applied to the value, a MIN DateTime value will be used in place of the null value e.g.: converting the DateTime to a ShortDate as described:
The number formatting was set to Date->01/31/2000 in the placeholder properties window. Pretty straightforward, nothing weird going on there. RIGHT?
To avoid this, the column value must be wrapped in an expression to conditionally apply the required formatting:
=IIf(IsNothing(Fields!DateTimeField.Value), "", FormatDateTime(Fields!DateTimeField.Value, DateFormat.ShortDate))

Answer 2

Use something like this in textbox expression:
=IIf(IsNothing(Fields!DateTime.Value), "", Fields!DateTime.Value)

Answer 3

It looks like there is no documentation to be found about this. The next best thing is to have this Q&A document things based on our collective experience.
Supposing the question: "What does SSRS do when displaying a DATETIME with a NULL value?"...
...the answer is it will display an empty string instead. There is no reproducible scenario where a NULL value would be displayed as anything else, unless you do some work to that end yourself, for example:
If the query COALESCEs the NULL to something else, e.g. the string "NULL" or a MIN DATETIME;
If you have an expression for the textbox value, e.g. IIF(Fields!MyDateTime.Value Is Nothing, "01-01-1900", Fields!MyDateTime.Value)

Answer 4

Every field returned in a SQL query gets a datatype assigned. Generally, you want to keep dates returned as dates from SQL, not as strings. (Don't format the date to a string in SQL. Do that as close to the presentation layer as possible.)
So instead of this in your query:
CASE WHEN ISNULL(l.SecondaryInjury, 0) = 0 THEN '' ELSE l.SecondaryInjuryDXDate END AS SecondaryInjuryRecordDate
I would try to use:
CASE WHEN ISNULL(l.SecondaryInjury, 0) = 0 THEN CAST( NULL AS DateTime ) ELSE l.SecondaryInjuryDXDate END AS SecondaryInjuryRecordDate
See SQL cast datetime for an explanation of why you are getting 0 cast to a date.

Answer 5

I did find when I format an entire column such as FormatDateTime(field, DateFormat.ShortDate) - SSRS will format that blank field to 01/01/0001. Just an FYI.