-NaN is a thing, but up to commit bb4853e414 has not been represented.

[Wall-AF]

Below details the commit and the fix.

D:\GIT_Sources\Ghidra.Latest\ghidra>git branch -a -vv
* master                     bb4853e414 [origin/master] Merge remote-tracking branch 'origin/Ghidra_11.3'

D:\GIT_Sources\Ghidra.Latest\ghidra>git diff -w **/BigFloat.java
diff --git a/Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/pcode/floatformat/BigFloat.java b/Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/pcode/floatformat/BigFloat.java
index 63967c0761..97269e0937 100644
--- a/Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/pcode/floatformat/BigFloat.java
+++ b/Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/pcode/floatformat/BigFloat.java
@@ -38,6 +38,8 @@ public class BigFloat implements Comparable<BigFloat> {
        public static final String POSITIVE_INFINITY = "+" + INFINITY;
        public static final String NEGATIVE_INFINITY = "-" + INFINITY;
        public static final String NAN = "NaN";
+       public static final String POSITIVE_NAN = "+" + NAN;
+       public static final String NEGATIVE_NAN = "-" + NAN;

        private static final int INFINITE_SCALE = -(64 * 1024);
        public static final BigDecimal BIG_POSITIVE_INFINITY =
@@ -1037,7 +1039,7 @@ public class BigFloat implements Comparable<BigFloat> {

        private String formatSpecialCase() {
                if (isNaN()) {
-                       return NAN;
+                       return sign < 0 ? NEGATIVE_NAN : POSITIVE_NAN;
                }
                if (isInfinite()) {
                        return sign < 0 ? NEGATIVE_INFINITY : POSITIVE_INFINITY;