\IfArgIsEmpty --> \IfIsEmpty

beamerinnerthemePTB.sty

-\ProvidesPackage{beamerinnerthemePTB}[2022/07/29 v 1.0.0 (RN)]
+\ProvidesPackage{beamerinnerthemePTB}[2022/07/31 v 1.0.0 (RN)]
 
 \mode<presentation>
 
@@ -14,7 +14,7 @@
         \vfill
         \usebeamerfont{title}\inserttitle
         \vfill
-        \Ifstr{\insertsubtitle}{}{\vfill}{%
+        \IfIsEmpty{\insertsubtitle}{\vfill}{%
           \usebeamerfont{subtitle}\insertsubtitle\\[3.5ex]
         }
         \usebeamerfont{author}\insertauthor\\[2ex]
@@ -52,12 +52,12 @@
               }%
               \\[1.3ex]%
               \begin{tabular}{@{}l@{~}l@{}}%
-              \multicolumn{2}{@{}l@{}}{\Ifstr{\PTB@contactName}{}%
+              \multicolumn{2}{@{}l@{}}{\IfIsEmpty{\PTB@contactName}%
                 {Max Mustermann}{\PTB@contactName}} \\
-              \translate{phone}: &
-              \Ifstr{\PTB@contactPhone}{}{0531 592-\#\#\#\#}{\PTB@contactPhone} \\
+              \translate{phone}: & 
+              \IfIsEmpty{\PTB@contactPhone}{0531 592-\#\#\#\#}{\PTB@contactPhone} \\
               \translate{email}: &
-              \Ifstr{\PTB@contactEMail}{}{Max.Mustermann@ptb.de}%
+              \IfIsEmpty{\PTB@contactEMail}{Max.Mustermann@ptb.de}%
                 {\PTB@contactEMail} \\  
               \end{tabular} \\
               \href{https://www.ptb.de}{www.ptb.de} \\[1.8ex]
@@ -115,7 +115,7 @@
               Braunschweig und Berlin \\
               \mdseries\translate{NMI}
             \end{varwidth}
-            \Ifstr{\PTB@orgLogo}{}{}{%
+            \IfIsEmpty{\PTB@orgLogo}{}{%
                \hfill\includegraphics[height=130\unitlength]{\PTB@orgLogo}%
             }
           \end{minipage}

beamerthemePTB.sty

-\ProvidesPackage{beamerthemePTB}[2022/07/29 v 1.0.0 (RN)]
+\ProvidesPackage{beamerthemePTB}[2022/07/31 v 1.0.0 (RN)]
 
 \mode<presentation>
 
@@ -34,6 +34,10 @@
   \fi
 }
 
+\newcommand\IfIsEmpty[3]{%
+  \Ifstr{#1}{}{#2}{#3}%
+}
+
 \newcommand*\finalpage[1][]{%
   \setkeys{PTB}{#1}%
   \global\@PTB@finalpagetrue