patch 8.0.0074
Problem:    Cannot make Vim fail on an internal error.
Solution:   Add IEMSG() and IEMSG2(). (Domenique Pelle)  Avoid reporting an
            internal error without mentioning where.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index f643329..1257aa0 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -2644,7 +2644,7 @@
 	    break;
 #endif
 	case VAR_UNKNOWN:
-	    EMSG2(_(e_intern2), "f_empty(UNKNOWN)");
+	    internal_error("f_empty(UNKNOWN)");
 	    n = TRUE;
 	    break;
     }
@@ -12695,7 +12695,7 @@
 	case VAR_JOB:     n = VAR_TYPE_JOB; break;
 	case VAR_CHANNEL: n = VAR_TYPE_CHANNEL; break;
 	case VAR_UNKNOWN:
-	     EMSG2(_(e_intern2), "f_type(UNKNOWN)");
+	     internal_error("f_type(UNKNOWN)");
 	     n = -1;
 	     break;
     }